Slow Cooker Green Bean Casserole

Combine fresh green beans, homemade mushroom cream sauce, and crispy fried shallots in your slow cooker for a flexible side that frees up your oven and schedule.

By
Brianne Ross
Brianne Ross Bio Photo
Brianne Ross
Brianne leads public and private programming focused on food education. She writes and develops recipes with a focus on seasonal cooking and sustainable eating. 
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Updated November 15, 2022
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Slow Cooker Green Bean Casserole on a Platter with Some on a Spoon

Simply Recipes / Ciara Kehoe

While I can’t deny the ease of opening a can of green beans and a can of mushroom soup and dumping them into a baking dish, taking a little extra time to prepare green bean casserole from scratch is well worth it and exponentially more delicious. Though green bean casserole is typically cooked in the oven, this version is made in a slow cooker, freeing up space it your oven. In the slow cooker, the green beans become very tender and soaked in the umami-packed mushroom cream sauce (made from scratch, of course).

The Flexibility of a Slow Cooker 

I love my slow cooker—it frees my hands (and oven) for hours, and the cook time is always forgiving. Fill it with ingredients, put the lid on, and let it do its thing. It doesn’t get much easier than that! 

Most slow cookers have three settings: high, low, and warm. I start most slow cooker recipes on high and reduce to low if I want to draw out the cook time. This recipe needs at least 2 hours on high to get the green beans tender, but cooking it for longer makes it even better—the flavors meld and the sauce cooks down and concentrates a bit more.

Then, I shift it to warm when everything inside is fully cooked, but I want to keep it warm until ready to serve. On the warm setting, the green bean casserole will hold for 4 to 5 hours, which is great for when your guests graze on the food throughout the party.

Small Bowl of Slow Cooker Green Bean Casserole Topped with Crispy Shallots

Simply Recipes / Ciara Kehoe

Using Fresh, Blanched Green Beans

You can use frozen green beans, but I recommend using fresh, if you have them. You will need to blanch them before adding them to the slow cooker. 

What is blanching? It means cooking the green beans in boiling water for a few minutes until they’re vibrantly colored and crisp-tender, then shock them in an ice bath—this stops any further cooking from residual heat and locks in the flavor.

You do not need to blanch frozen green beans.

A Simple Homemade Mushroom Cream Sauce

I have a friend who is a diehard fan of classic green bean casserole—only store-bought French’s Fried Onions sprinkled on top scratch that nostalgic itch for her. But even she admits that homemade mushroom cream sauce is a game changer and far more delicious than the canned stuff. And it couldn’t be simpler to make. 

Start by cooking your mushrooms in a bit of butter. I typically use cremini mushrooms—they are small, tender, and have a subtle meaty flavor., You can use a mix of mushrooms: button, portobello, chanterelle, and even a few morels would be delicious. I’d avoid shiitake mushrooms because they are too chewy for this recipe.

Once the mushrooms are cooked, add a bit of flour to make a roux—a combination of butter and flour used to thicken the sauce—and then add some chicken stock and cream. That's it!

The mushroom sauce can be made ahead and stored in the fridge for up to 5 days or in the freezer for 2 months. 

Green Bean Casserole in a Slow Cooker Topped with Crispy Shallots and Next to It, a Small Plate with More Shallots and a Kitchen Towel

Simply Recipes / Ciara Kehoe

Fry Your Own Shallots

I prefer crispy shallots to onions on top of my green bean casseroles—they are crispier when fried and don't even need a batter. without a batter. 

The trick to ultra crispy shallots is to slice them as thinly as possible. Start them in cold oil. They'll get crispy in no time, so stir them regularly and keep a close eye on them. Once they become golden brown, drain the fried shallots on a paper towel. And try not to snack on too many while your casserole cooks! 

The fried shallots can be stored in an airtight container for up to 1 month. 

Simple Tip!

Save the shallot oil. It’s delicious for everything from sautéing vegetables to whisking into salad dressing.

Don’t have time to fry your own shallots? I keep a jar of store-bought shallots in my cupboard at all times. I find them at my local Asian grocery store. Of course, French’s Fried Onions always works too.

Swaps and Substitutions

  • This recipe uses chicken stock, but you can easily make it vegetarian by swapping out vegetable stock or, even better, mushroom stock.
  • Looking for a vegan casserole? Use vegan butter, like Earth Balance, and unsweetened cashew milk instead of the half and half. 
  • Is it a green bean casserole without green beans? Probably not. But blanched broccoli or cauliflower would be delicious swaps regardless. 
Slow Cooker Green Bean Casserole Topped with Crispy Shallots on a Platter Surrounded by Utensils, a Kitchen Towel, and a Glass of Water

Simply Recipes / Ciara Kehoe

For the Love of Green Beans

Slow Cooker Green Bean Casserole

Prep Time 40 mins
Cook Time 2 hrs 30 mins
Total Time 3 hrs 10 mins
Servings 8 to 10 servings

Ingredients

  • 2 pounds green beans, trimmed and cut into 1 1/2-inch pieces

  • 3 tablespoons unsalted butter, divided

  • 1 pound sliced cremini mushrooms

  • 2 teaspoons salt, plus more to taste

  • 3 garlic cloves, minced 

  • 1 tablespoon fresh thyme leaves

  • Large pinch crushed red pepper flakes

  • 1/4 cup all-purpose flour

  • 1 1/2 cups chicken stock

  • 1 1/2 cups half and half

  • 1 teaspoon soy sauce

  • 1 teaspoon red wine vinegar

  • A few cracks freshly ground black pepper

For the crispy shallots

  • 1 pound (about 8 medium) shallots, very thinly sliced

  • 2 cups vegetable oil

Method

  1. Prep for blanching the green beans: 

    Fill a large stock pot or Dutch oven with heavily salted water and set on the stove to boil over high heat. 

    Fill a large mixing bowl with ice water and set aside (this is your ice bath).

    Bowl of Ice Water and a Pot of Boiling Water Situated Next to Each Other for Slow Cooker Green Bean Casserole

    Simply Recipes / Ciara Kehoe
  2. Blanch the green beans:

    Once the water comes up to a boil, add the green beans and cook until bright green and just tender, 4 to 5 minutes.

    Drain the green beans and immediately plunge them into the ice bath. Once cooled, drain the green beans again and set aside.

    Green Beans Blanched in Pot of Boiling Water for Slow Cooker Green Bean Casserole

    Simply Recipes / Ciara Kehoe
    Blanched Green Beans in Bowl of Ice Water for Green Bean Casserole in a Slow Cooker

    Simply Recipes / Ciara Kehoe
  3. Sauté the mushrooms:

    In the same pot or Dutch oven, melt 2 tablespoons butter over medium heat. Once melted, add the mushrooms and the salt. Cook the mushrooms until they’ve softened and any water they’ve released has cooked away, about 8 minutes.

    Mushrooms Sautéed in a Pot for Slow Cooker Green Bean Casserole Recipe

    Simply Recipes / Ciara Kehoe
  4. Add garlic and red pepper flakes:

    Add the remaining butter, garlic, thyme leaves, and red pepper flakes, and cook until the garlic is fragrant, about 1 minute.

    Seasoning and Garlic Added to Cooked Mushrooms for Green Bean Casserole in a Slow Cooker Recipe

    Simply Recipes / Ciara Kehoe
  5. Finish the mushroom sauce:

    Sprinkle the flour over the mushrooms and stir to coat. Slowly add the chicken stock and half and half, making sure to scrape the bottom of the pot to scrape up any stuck-on bits. Cook, stirring frequently, until the sauce has reduced and thickened, about 10 minutes.

    Add the soy sauce, red wine vinegar, and a few crack of black pepper. Stir well and taste the sauce, you may want to add more salt.

    Mushroom Sauce Stirred in a Pot for Slow Cooker Green Bean Casserole Recipe

    Simply Recipes / Ciara Kehoe
  6. Assemble the casserole in the slow cooker:

    Add the blanched green beans and mushroom sauce into the slow cooker. Stir until the green beans are coated in the sauce. Cover with a lid and cook on high for 2 1/2 hours, until the green beans are soft and tender, but not mushy.

    Green Bean Casserole Ingredients Added to Slow Cooker

    Simply Recipes / Ciara Kehoe
  7. Prep for frying:

    Line a large plate with several pieces of paper towel. Set a fine-mesh strainer over a heat-proof bowl. Set both aside.

    A Colander Placed on a Bowl and a Plate Covered in Paper Towels for Slow Cooker Green Bean Casserole

    Simply Recipes / Ciara Kehoe
  8. Fry the shallots:

    In a medium saucepan, combine the sliced shallots and vegetable oil. Cook on medium-low heat, stirring frequently. The shallots will soften first and then turn golden brown. Continue to fry until the shallots are a dark golden brown, about 20 minutes. Carefully strain the shallots through the fine-mesh strainer and then spread them out on the prepared paper-towel lined plate to cool.

    Simple Tip!

    Reserve the flavorful shallot oil for dressings and cooking.

    Crispy Shallots Cooling on a Paper Towel Lined Plate

    Simply Recipes / Ciara Kehoe
  9. Serve the casserole:

    Once the green beans are cooked, stir them well and set the slow cooker to warm. Scatter the fried shallots on top and serve.

    I store my leftovers directly in the slow cooker—just put the lid on and clear some room in the fridge—for up to 5 days.

    To reheat, return the pot to the base and heat on low for about 1 hour.

    Did you love the recipe? Leave us stars below!

    Green Bean Casserole in a Slow Cooker Topped with Crispy Shallots

    Simply Recipes / Ciara Kehoe
Nutrition Facts (per serving)
268 Calories
19g Fat
21g Carbs
6g Protein
Show Full Nutrition Label Hide Full Nutrition Label
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Nutrition Facts
Servings: 8 to 10
Amount per serving
Calories 268
% Daily Value*
Total Fat 19g 24%
Saturated Fat 6g 29%
Cholesterol 23mg 8%
Sodium 535mg 23%
Total Carbohydrate 21g 8%
Dietary Fiber 5g 16%
Total Sugars 9g
Protein 6g
Vitamin C 13mg 65%
Calcium 108mg 8%
Iron 2mg 9%
Potassium 565mg 12%
*The % Daily Value (DV) tells you how much a nutrient in a food serving contributes to a daily diet. 2,000 calories a day is used for general nutrition advice.
Nutrition information is calculated using an ingredient database and should be considered an estimate. In cases where multiple ingredient alternatives are given, the first listed is calculated for nutrition. Garnishes and optional ingredients are not included.