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This Slow Cooker Green Bean Casserole is a great mix of convenience and from-scratch cooking and won’t take up any oven space. Start with frozen beans but make your own creamy mushroom sauce, then top the whole thing with plenty of crunchy fried onions.
I didn’t grow up eating Green Bean Casserole at Thanksgiving, but based on the recipe I see in Campbell’s magazine ads, I’m not sorry about it. Canned green beans with canned mushroom soup? I’m not a food snob, but that just doesn’t sound like my kind of thing.
So when I made Green Bean Casserole the first time, I kicked the cans. I’ve made Green Bean Casserole in the oven with fresh beans too, but my go-to is this version, in a slow cooker, with frozen green beans.
The Cream of Mushroom sauce takes about 10 minutes or so, and it’s worth every second. The flavor here is so much better than canned: Rich, savory mushrooms, heavy cream, and fresh garlic.
Toss the green beans in the sauce, then transfer the whole thing to your slow cooker. Just before serving, top the Green Bean Casserole with crispy French fried onions. Yes, those classic crunchy ones from a can. If it ain’t broken, don’t fix it.
Table of Contents
Recipe ingredients
At a Glance: Here is a quick snapshot of what ingredients are in this recipe.
Please see the recipe card below for specific quantities.
Ingredient notes
- Mushrooms: Use fresh mushrooms to make a quick from-scratch cream of mushroom sauce.
- Frozen green beans: To substitute fresh beans, trim and chop 2 pounds of green beans. Blanch the beans in 4 quarts of boiling salted water for about 5 minutes, then drain well and plunge immediately in to an ice bath to stop the cooking.
- Fried onions: To substitute bread crumbs for the canned fried onions, pulse 4 slices hearty white bread (torn into pieces) in a food processor or blender. You will have about 3 cups of crumbs. Stir in 3 tablespoons melted butter or olive oil and fry in a large skillet over medium-high heat until browned. Sprinkle over the casserole just before serving.
Step-by-step instructions
- In a large skillet or Dutch oven, melt butter over medium-high heat until foaming subsides. Add mushrooms, garlic, ¾ teaspoon salt, and ⅛ teaspoon pepper. Cook until the mushrooms have released most of their liquid, about 5 to 7 minutes.
- Stir in flour and cook for one minute. Whisk in broth, scraping up any brown bits from the bottom of the pan. Bring to a boil, whisking constantly.
- Reduce heat to medium. Whisk in cream and simmer until the sauce has thickened, about 5 minutes. Season to taste with salt and pepper.
- Meanwhile, cook the beans in the microwave according to the package instructions (or microwave on HIGH power for 4 to 5 minutes; let stand 1 minute before removing from the microwave). Drain well (I like to use a salad spinner to spin them dry). Add the green beans to the pot with the mushroom sauce and toss until evenly coated. Transfer the beans and sauce to a crock pot.
- Cook on HIGH for 2 hours or LOW for 4 hours or until a thermometer inserted in to the middle of the casserole reaches 165 degrees. Top with canned fried onions immediately before serving.
Recipe tips and variations
- Yield: This recipe makes about 10 cups of casserole, enough for 10 1-cup sized, side dish (you’ll be able to feed more than 10 people depending on how many sides you have at Thanksgiving).
- Storage: Store leftovers covered in the refrigerator for up to 4 days.
- Make ahead: You can make the mushroom sauce up to 2 days before. Cool and refrigerate. Since the sauce will be going in cold, increase the crockpot time to 3 hours on HIGH or 5 hours on LOW.
- Blanch fresh green beans ahead: If using fresh beans instead of frozen, they may be blanched the night before, cooled, and stirred in the cooled mushroom sauce, and refrigerated overnight. Increase the crockpot time to 3 to 4 hours on HIGH or 5 to 6 hours on LOW .
- Oven instructions: Follow the recipe as written through Step 5, but then instead of transferring the green bean mixture to a slow cooker, spread it in the bottom of a 3-quart or a 9×13 baking dish. Sprinkle with fried onions and bake at 425 degrees until the top is golden brown and the sauce is bubbling around the edges, about 15 minutes.
- Small batch: Green bean casserole for two is made in the oven with 8 ounces frozen green beans.
- Vegan Green Bean Casserole: Plant-based Green Bean Casserole made with cashew cream in a slow cooker.
- Small army: To triple the recipe for 30 to 40 people, increase the ingredients as follows: ½ cup (1 stick) butter, 3 pounds white button mushrooms, 1 bulb garlic (9 to 10 cloves) 3 teaspoons salt, and ½ teaspoon pepper, 1 cup flour, 4 ½ cups chicken broth, 4 ½ cups heavy cream, 6 (12-ounce) packages of frozen cut green beans, and 3 cups canned fried onions (or more if desired).
- Best Thanksgiving Slow Cooker Recipes: Discover the best slow cooker recipes for your Thanksgiving feast including turkey and all the classic sides. Free up oven and stove top space when you need it most by cooking one (or more!) Thanksgiving recipes in a crockpot.
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Slow Cooker Green Bean Casserole
Ingredients
- 3 tablespoons butter
- 1 pound white button mushrooms sliced (see note 1)
- 3 cloves garlic minced
- salt and freshly ground black pepper
- 3 tablespoons all-purpose flour
- 1 1/2 cups chicken broth
- 1 1/2 cups heavy cream
- 2 (12 ounce) packages frozen cut green beans (see note 2)
- 3 cups canned fried onions (see note 3)
Instructions
- In a large skillet or Dutch oven, melt butter over medium-high heat until foaming subsides. Add mushrooms, garlic, ¾ teaspoon salt, and ⅛ teaspoon pepper. Cook until the mushrooms have released most of their liquid, about 5 to 7 minutes.
- Stir in flour and cook for one minute. Whisk in broth, scraping up any brown bits from the bottom of the pan. Bring to a boil, whisking constantly.
- Reduce heat to medium. Whisk in cream and simmer until the sauce has thickened, about 5 minutes. Season to taste with salt and pepper.
- Meanwhile, cook the beans in the microwave according to the package instructions (or microwave on HIGH power for 4 to 5 minutes; let stand 1 minute before removing from the microwave). Drain well (I like to use a salad spinner to spin them dry).
- Add the green beans to the pot with the mushroom sauce and toss until evenly coated. Transfer the beans and sauce to a crock pot.
- Cook on HIGH for 2 hours or LOW for 4 hours or until a thermometer inserted in to the middle of the casserole reaches 165 degrees. Top with canned fried onions immediately before serving.
Recipe Video
Notes
- Mushrooms: Use fresh mushrooms to make a quick from-scratch cream of mushroom sauce.
- Frozen green beans: To substitute fresh beans, trim and chop 2 pounds of green beans. Blanch the beans in 4 quarts of boiling salted water for about 5 minutes, then drain well and plunge immediately in to an ice bath to stop the cooking.
- Fried onions: To substitute bread crumbs for the canned fried onions, pulse 4 slices hearty white bread (torn into pieces) in a food processor or blender. You will have about 3 cups of crumbs. Stir in 3 tablespoons melted butter or olive oil and fry in a large skillet over medium-high heat until browned. Sprinkle over the casserole just before serving.
- Yield: This recipe makes about 10 cups of casserole, enough for 10 1-cup sized, side dish (you’ll be able to feed more than 10 people depending on how many sides you have at Thanksgiving).
- Storage: Store leftovers covered in the refrigerator for up to 4 days.
- Make ahead: You can make the mushroom sauce up to 2 days before. Cool and refrigerate. Since the sauce will be going in cold, increase the crockpot time to 3 hours on HIGH or 5 hours on LOW.
Nutrition
Meggan Hill is a classically-trained chef and professional writer. Her meticulously-tested recipes and detailed tutorials bring confidence and success to home cooks everywhere. Meggan has been featured on NPR, HuffPost, FoxNews, LA Times, and more.
This recipe was awesome, we tripled it for a large group on Thanksgiving and everyone loved it!
Question- we didn’t end up using all of the mushroom/cream sauce that we made, do you have any suggestions for how to use the rest of it? Is it basically just homemade cream of mushroom soup or not because of the cream in it….
Hi Kristen, thank you so much for writing! I’m so happy it was a hit! Readers have used it in tuna casserole, but it could work for other casseroles as well. It could also be used as a base for the filling of a pot pie, or be made into a beef stroganoff-type dish. I hope this helps! Take care! – Meggan
Hi Meggan, two questions. Regarding subbing coconut milk, would you use canned or the liquid in a carton in dairy section? Second, I need to use oven at 350 for dressing, approximately how long to oven bake at lower temp?
Thanks for your help!
Hi Penny, thank you for your questions! I would probably use the canned coconut milk instead of the carton variety since it is thicker, and closer to heavy cream. Baking time at 350 degrees should be about 25 to 30 minutes, but I would check in on it around 20 minutes. Please write with any more questions! Take care, Penny! – Meggan
Could I make the mushroom sauce more than 4-5 days in advance and freeze it?
Hi Kristi, I haven’t tried freezing this soup, but other readers have and love it. It would be possible the texture will change some, so it may need a quick whisking to smooth out. Make sure to leave headspace for it to expand. Take care! – Meggan
Love this recipe. They were delicious. So good. Thank you!
You’re welcome, Lucinda! So glad you loved it! – Meggan
I made this recipe to take to our family Thanksgiving get-together. It was excellent and everyone enjoyed it. My comment is about a recommendation from you in the directions. They said to microwave frozen green beans and drain them well. my complaint / suggestion for the future is to NOT use a salad spinner to spin them dry if you buy French Cut Green Beans!. Using the salad spinner probably would be fine for regular cut beans.
However, lots of the small pieces of the French Cut Beans got trapped in the tiny openings of the salad spinner. They did not even rinse out!
I finally had to use a tweezer to get them all out, which took almost an hour!
Hi Sherri, I’m glad everyone enjoyed the recipe! As for the salad spinner, I’m so sorry that happened to you. I’ve never run into this issue but thank you for the warning in case any other readers run into the same problem. – Meggan
I will be making this on Thursday but for a smaller group. If I’m using 1 lb of fresh green beans and cutting the recipe in half, would it cut the cooking time in half?
Hi Debra, great question! The cooking time likely would be less, depending on what size slow cooker you use. I usually make this in a 6-quart slow cooker, but if I were going to do a smaller batch, I would use a smaller slow cooker so the cooking times would be closer to the recipe. Slow cookers’ power and sizes vary so much. I would keep an eye on it, and turn it to warm to hold until you’re ready to serve. Enjoy! – Meggan
I have never made a green bean casserole before. This recipe sounds good. I would like to use fresh green beans. How many pounds do you recommend for your recipe?
Hi Julie, I’m so sorry that I didn’t have that information in the recipe! I was actually shocked, I have all this information about HOW to substitute fresh green beans, but not HOW MANY fresh green beans to use! So silly. It’s 2 pounds of fresh green beans, that’s what you want. I’m so sorry about that! Also, after you trim the fresh green beans, I recommend cutting them in half (not lengthwise, just like chopping them in half so they are the same size as frozen beans). Good luck and sorry again! I’m going to go add that to the post right now. -Meggan
Meggan,
Reviewing your recipe I noticed no fried onions rings were mixed in with the beans and the sauce. Is this because they get toooo mushy and better to just put on top just before serving? Also, if I do that would it be best to put the casserole from the slow cooker in the oven and toast the onions for about 10 minutes at 350?
Thanks….Beverly
P.S. Loved your mother’s comment….I grew up in the midwest and my mother always said the same thing……6 of 1…half a dozen of the other
Hi! Yes! Your thoughts are exactly right. They would get too mushy (for my liking anyway)! You can absolutely bake it longer to toast the onions, I just never have room in my oven for that, and I think they’re fine as is. I sometimes even sneak hand fulls out of the can! 🙂 Happy Thanksgiving Beverly!
Hello! Thanks for the recipe. Can’t wait tio try it. I was just wondering what size crock pot you are using and if I increase servings to 20 people, will a 6 qt crockpot work? Thank you!
Hi Jennifer, you should be fine with this, but it may be close. I would definitely recommend mixing the green beans in the mushroom sauce in a very big bowl AND THEN add it to the crock pot. I think it might just get messy if you try to do all the mixing in the crock pot. If they don’t all fit, you can always store the remaining in the fridge and bake them (but who has oven space for that). I added the baking instructions to the recipe card a few days ago because someone else requested it. Hopefully it works for you- fingers crossed! -Meggan
Hi! This sounds great! Is there a way to make this in the oven as well?
Thanks!
Hi Laura, yes definitely! I had adapted this from a Cook’s Illustrated recipe to make the slow cooker version, but their recipe was originally made in the oven. Everything is the same through the part where you toss the beans in the sauce. Then, instead of transferring that to a slow cooker, spread it in the bottom of a 3-quart OR a 9×13 baking dish. Sprinkle with the topping and bake at 425 degrees until the top is golden brown and the sauce is bubbling around the edges, about 15 minutes. I hope this helps! Thank you! -Meggan
We will be traveling 4hours to our destination on the day before Thanksgiving. I plan on making the mushroom sauce and thawing the beans ahead of time. Would it be best to assemble the casserole or put it in separate containers and then assemble it Thanksgiving morning? Also, I will be doubling the recipe…..will I need more cooking time?
Thanks for your help…..Happy Thanksgiving!
Beverly
Hi Beverly, it doesn’t really matter if you assemble it ahead of time or not. As my mom would say – 6 of 1, half a dozen of the other. I would say if you want to transport it unassembled, you could leave the beans frozen (they will thaw on the way). You’ll need a cooler either way unless everything is frozen solid.
As for doubling the recipe… I’ve only tripled it, not doubled it. Here are the instructions for tripling. What you’ll need to do will fall somewhere between this and the original. The actual SLOW COOKER time isn’t increased, just the ingredients for making more sauce.
Cook the mushrooms for about 10 minutes in Step 2 and simmer the sauce for 10 minutes in Step 3. Cook on HIGH for 2 hours or LOW for 4 hours (or until a thermometer reaches at least 165 degrees in the middle of the casserole). Add more canned onions throughout serving time if the top layer is depleted, if desired.
I hope this is helpful! If you need more info, just let me know. Thanks! -Meggan
Just made over the holidays for a family dinner…..I love using the crockpot (and liners) to help with clean up at the end and to not have too many things going on around meal time. Everyone, including the little ones, was a fan and it was gone by the end of the night. I mixed in some of the fried onions into the green beans ahead of time and let them all cook and get comfy together. PERFECT.Â
Can you double this recipe? I think the tripled version is going to be too much, but since it requires some changes to the recipe, I’m curious if that goes for doubling too. I’ve only ever made the single version and love it!!!
Hi Ellen – YES! I’ve doubled it and it still fit in my crockpot. And it was amazing. Feel free to mix in more of the fried onions too – that’s what I did. 😀 Happy Thanksgiving! -Meggan
So I came across this recipe because I was looking at making cream of mushroom from scratch. You have a recipe for condensed cream of mushroom that is slightly different than this recipe calls for. It seems the condensed soup you made has a bit more depth to it. Would I just add water to that one and substitute it for what is in this one? What are you recommendations? Thanks in advance.
Hi Chris! Yes, this recipe is basically the cream of soup in the un-condensed version. I think (but maybe I’m wrong) that if you make traditional green bean casserole, you would add some sort of liquid to it to thin out the canned cream of soup. So my recipe basically factors that in. But in the event that I’m wrong, or you just want to use the condensed version, I would make the sauce with the condensed soup and just see what you think. Make it, taste it, throw it all together, if it seems too thick you could add water, chicken stock, milk, whatever you want. Does that make sense? I’d make it and go with your gut, literally and figuratively. I hope this helps. If you have other questions just let me know! -Meggan
I would like to cut back on the milk added, as I cannot tolerate it very well. Could I add whole milk and broth? I think I would need to add more flour to make sure it thickens enough, do you think?
Hi Lee, I do think you could probably substitute whole milk and use more flour (how much, I’d have to test to see). However, my gut reaction is to suggest a milk substitute such as coconut cream. The thick one. I can test it that way in the next day or so. Do you have a preference? Just let me know!
Hi Meggan,
Thanks for the response. I would be afraid the coconut would taste weird, but I did think about using maybe plain Greek yogurt instead. What do you think?
Hi Lee, I once had a casserole with the coconut cream and you never would have known it was coconut cream. So that’s the only reason I suggested it… but I completely understand your fears. I am not sure how Greek Yogurt would work. It might work perfectly, but I just have no idea! I haven’t used it as a thickener before. If you think you can tolerate the whole milk, that is within the realm of my experience. I would just go with equal parts fat (butter) and flour, you can always add more milk if it’s too thick. And if it’s too thin, you mash up more butter and flour in your hand (cold) and toss it in to the hot sauce and whisk it.
Well thank you for figuring out a way to skip the canned soup on this recipe. We make this every year but I never really like using the canned soup either . . . but it’s Thanksgiving so we keep making it anyway . . . so thanks for the breakthrough! I made your Chipotle copycat guacamole at lunch today, and I made the salsa the other night . . . I LOVE that salsa!!!
Hey Julie! Thanks so much for your comment. I personally think Green Bean Casserole is MUCH better without the canned cream of soup. The real thing isn’t too hard to make, either! But I know what you mean, it’s hard to break tradition. 🙂 Also, thanks for trying the Chipotle Guacamole! And the salsa! I appreciate you. 🙂 Take care!
How many people/servings does your recipe make? I like the idea of making your own mushroom sauce. I will be hosting approximately 30 people for Thanksgiving, so I want to have enough. THANKS.
Hi Liz! This recipe makes 8 to 10 servings. I feel like you could triple the recipe and be fine. I will test it out this weekend (tripling the recipe) and leave you another comment (and update the post) with any changes. I’ve been wanting to make this again anyway! Thanks for your question!
Hey Liz! I tripled the recipe yesterday and it worked just great. I updated the blog post with the info (the increased ingredient amounts and instructions are in the recipe notes). If it’s easier, I can shoot you an email with the updated info. Just let me know! You just need a 5.5 quart stock pot AND a 6.5 quart slow cooker to accommodate the increase in ingredients. Please let me know if you have any questions! Thanks again!
Can you use half-n-half in place of the heavy cream?
Myra, yes! Absolutely. That’s how my mom makes it. 🙂 Thank you for your question!!
Love at first read! I love green bean casserole, so this tad bit healthier version was right up my alley. Next year I plan on makin my own fried onions. Two things I did add were sunflower kernals and cream cheese. YUMMY! Thanks so much for revamping an old classic!
Maybe just “a tad” bit healthier because not really. 😀 That’s awesome if you make your own fried onions, I just can’t do it. Not that hardcore. CREAM CHEESE?! Yes, oh yes. And even sunflower kernels sound amazing!!! Great ideas, thank you for sharing!
I’ve actually never had green bean casserole before! I’m obsessed over how cheap green beans are so I’ve been trying to cook more with them haha. IF I wasn’t sold by the photos I was definitely pinning by the time you said this was the sexy julia roberts of food;)
Oh, this is one of my favorite meals. Love it! Never made it in a crock pot though. Need to make is pretty soon.
Oooh … delicious! I’ve said this before (a few times!) but I really am enjoying learning about your traditional foods. We don’t have anything like this over in the UK. We did have similar sorts of ‘bakes’ in the 80s/90s made with the Campbells thick soup, though, and I always loved it. Great to have a ‘real’ recipe for it and, for me, the piece de resistance is definitely those crispy onions. Mmm!
We do not have cans of fried onions here in Australia, so what could I use instead??
Hi Pauline, making any kind of onion rings/onion strings from scratch would be the closest substitute, but that’s likely WAY too much work and kind of defeats the purpose of this recipe. Using crunchy, buttery bread crumbs is equally delicious.
1. Preheat the oven to 350 degrees F/175 degrees C.
2. Pulse 4 slices white sandwich bread (torn into quarters), 2 Tablespoons softened unsalted butter, 1/4 teaspoon salt, and 1/8 teaspoon pepper in a food processor until it resembles coarse crumbs (about 10 pulses).
3. Spread the bread crumbs in an even layer on a rimmed baking sheet. Bake until lightly golden brown, about 10 to 15 minutes.
4. Add them to the slow cooker right at the end, in place of the canned fried onions.
5. You can make them ahead of time and store them in the refrigerator, but you may want to return them to the oven to warm up for a few minutes before you add them to the crock pot. Straight out of the fridge, obviously, they’d be cold.
Thanks so much for your question! I will definitely update the recipe to include the bread crumbs option. If you have anymore questions, just let me know!
I don’t have a microwave. Would I just follow the stovetop cooking instructions on the package for the frozen beans? Or I am wondering if I could just defrost them overnight in the refrigerator, drain any extra water and add to the sauce. Won’t the crockpot cook them sufficiently without the extra step?
Hi Mary, thanks for your question! I think you could do either. The main point of cooking them/thawing them ahead of time is to get rid of the excess water. Â I tried putting them in the crockpot straight from the freezer, and they watered down the sauce in the process. So, either cooking them on the stove top or thawing them overnight (and draining well in either case) should do the trick. Thanks for your question and I’ll add some notes about this in the post so it’s clear for everyone else!