This Slow Cooker Green Bean Casserole is made from scratch, can easily be made ahead, and won’t taken up any space in your oven on Thanksgiving.

Slow cooker green bean casserole on a black and white serving platter with a serving spoon and fork.
Table of Contents
  1. Recipe ingredients
  2. Ingredient notes
  3. Step-by-step instructions
  4. Recipe tips and variations
  5. Slow Cooker Green Bean Casserole Recipe

Recipe ingredients

Slow cooker green bean casserole ingredients labeled and in various bowls.

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

  1. In a large skillet, melt the butter over medium-high heat until the foaming subsides. Add the sliced mushrooms, garlic, and some salt and pepper. Cook the mushrooms, stirring occasionally, until they release their liquid. Then stir in the flour and cook about a minute longer.
Mushrooms cooking down in a stock pot.
  1. Whisk in the broth and scrape up any brown bits on the bottom of the pan. Bring the mixture to a boil, stirring constantly. Then reduce the heat to medium.
Adding chicken broth to cooked mushrooms.
  1. Whisk in the cream and simmer until thickened, about 5 minutes. Season to taste with salt and pepper. Remove from heat and use immediately, or let cool and refrigerate overnight.
Adding cream to mushroom soup.
  1. Cook the green beans in the microwave according to the instructions on the package (or on HIGH power for 4 to 5 minutes). Drain well and add the green beans to the crock pot and cover with the mushroom sauce. Gently toss until combined.
Slow cooker green bean casserole ingredients in a black slow cooker.
  1. Cover and cook on HIGH for 2 hours or LOW for 4 hours. Before serving, check the temperature; the center of the casserole should be 165 degrees. Sprinkle with canned fried onions and serve immediately.
Slow cooker green bean casserole on a black and white serving platter with a serving spoon and fork.

Recipe tips and variations

  • Yield: This recipe makes enough for 10 as a side dish (or more depending on how many sides you have at Thanksgiving).
  • Make the mushroom sauce ahead: Cool and refrigerate overnight. 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 .
  • Storage: Store leftovers in the refrigerator for up to 4 days.
  • 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.
  • 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).

More Thanksgiving recipes

Green bean casserole on a platter.

Slow Cooker Green Bean Casserole

This Slow Cooker Green Bean Casserole is made from scratch, can easily be made ahead, and won't taken up any space in your oven on Thanksgiving.
5 from 15 votes
Prep Time 5 mins
Cook Time 2 hrs 20 mins
Total Time 2 hrs 25 mins
Servings 10 servings
Course Side Dish
Cuisine American
Calories 280

Ingredients 

  • 3 tablespoons butter
  • 1 pound white button mushrooms wiped clean, sliced or broken into pieces (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 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

  1. Mushrooms: Use fresh mushrooms to make a quick from-scratch cream of mushroom sauce.
  2. 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.
  3. 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.
  4. Yield: This recipe makes enough for 10 as a side dish (or more depending on how many sides you have at Thanksgiving).
  5. Make the mushroom sauce ahead: Cool and refrigerate overnight. Increase the crockpot time to 3 hours on HIGH or 5 hours on LOW.
  6. 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 .
  7. Storage: Store leftovers in the refrigerator for up to 4 days.
  8. 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.
  9. Small batch: Green bean casserole for two is made in the oven with 8 ounces frozen green beans.
  10. 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).

Nutrition

Calories: 280kcalCarbohydrates: 12gProtein: 3gFat: 25gSaturated Fat: 14gTrans Fat: 1gCholesterol: 58mgSodium: 315mgPotassium: 207mgFiber: 1gSugar: 1gVitamin A: 632IUVitamin C: 4mgCalcium: 30mgIron: 1mg
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Meggan Hill

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Comments

  1. 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?

    1. 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

  2. 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?

    1. 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

  3. 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

    1. 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!

  4. 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!

    1. 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

    1. 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

  5. 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!
    Beverly5 stars

    1. 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

  6. 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. 5 stars

  7. 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!!!

    1. 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. :D Happy Thanksgiving! -Meggan

  8. 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.5 stars

    1. 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

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