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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).
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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.
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