How To Make Green Bean Casserole with Frozen Green Beans

updated Oct 10, 2023

Learn how to make green bean casserole using the right grocery store shortcuts to rival the classic back-of-the-box recipe.

Serves8 to 10

Prep10 minutes

Cook25 minutes to 30 minutes

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“Classic” green bean casserole can mean a lot of different things, depending on who you ask. The quickest green bean casseroles are assembled from store-bought ingredients and offered as the token green vegetable side dish for holiday dinners. While others include scratch-made components (fresh green beans! homemade mushroom sauce! freshly fried onions!).

Why not take the best bits from both extremes? This green bean casserole balances convenience and quality thanks to frozen green beans, a velvety from-scratch mushroom cream sauce, and everyone’s favorite store-bought crispy onions. Here’s how to make the best green bean casserole with frozen green beans.

Credit: Joe Lingeman

Why You Should Use Frozen Green Beans

My mother always made green bean casserole with store-bought canned green beans because that’s what her mother did. When I make green bean casserole, I skip canned beans all together. Frozen green beans are the best green beans to use for green bean casserole.

Frozen green beans are blanched and flash-frozen to preserve their peak-season flavor. Simply thaw and drain the green beans before adding to the casserole — otherwise their excess moisture may thin the mushroom gravy.

(Image credit: Joe Lingeman)

How to Make Mushroom Sauce for Green Bean Casserole

Old-school green bean casserole uses condensed mushroom soup— an ode to the marketing geniuses at Campbell’s and French’s responsible for popularizing the dish. Luckily, a homemade mushroom sauce is simple, more flavorful, and affordable. Here are a few keys to success.

  • Be patient with the mushrooms: Cook the mushrooms until they brown and release most of their moisture. Mushrooms have more water in them than you’d think. This takes about five minutes over medium-high heat.
  • Wait for the nutty smell: Sprinkle the flour over the mushrooms and cook until the flour smells nutty, stirring regularly. This will help thicken the sauce.
  • Keep stirring: Add the milk and broth slowly and stir while mixing to prevent lumps. Bring the whole thing to a simmer and make sure it thickens in the pan. Remember that it will continue to thicken as it cools.
  • A surprise ingredient: A teaspoon of soy sauce or tamari adds that super-savory flavor and color we expect from condensed mushroom soup. You can certainly skip it, but be sure to taste the gravy and add more salt if needed.
(Image credit: Joe Lingeman)

What is the Best Topping for Green Bean Casserole?

Canned fried onions are the way to go. I have tried every method for making crispy onions for green bean casserole, from roasting breadcrumb-rolled rings to frying tempura-style onions to dehydrating onions until crisp. But no other onion comes close to the ease and flavor of the canned fried onions.

How to Make Green Bean Casserole in Advance

  • Up to three days before: Assemble the casserole without the crisp onion topping and store tightly wrapped in the refrigerator for up to three days.
  • While the oven preheats: Remove the assembled casserole from the refrigerator to take some of the chill off while the oven heats up.
  • Just before baking: Top with the fried onions and bake according to instructions.

How To Make Green Bean Casserole with Frozen Green Beans

Learn how to make green bean casserole using the right grocery store shortcuts to rival the classic back-of-the-box recipe.

Prep time 10 minutes

Cook time 25 minutes to 30 minutes

Serves 8 to 10

Nutritional Info


  • 1 1/2 pounds

    frozen green beans

  • 12 ounces

    white button or cremini mushrooms

  • 2 cloves


  • 4 tablespoons

    (1/2 stick) unsalted butter

  • 1/4 cup

    all-purpose flour

  • 2 cups

    whole milk

  • 1 cup

    low-sodium chicken or vegetable broth

  • 1 teaspoon

    tamari or soy sauce

  • 1/2 teaspoon

    freshly ground black pepper

  • 1/2 teaspoon

    freshly grated nutmeg

  • 2 (6-ounce) cans

    fried onions, such as French's Fried Onions, divided


  • Measuring cups and spoons

  • Chef's knife

  • Cutting board

  • Straight-sided skillet

  • 9x13-inch baking dish

  • Spatula or wooden spoon


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  1. Heat the oven to 325ºF. Arrange a rack in the middle of the oven and heat the oven to 325°F.

  2. Prepre the vegetables. Thaw and drain any excess liquid from 1 1/2 pounds frozen green beans. Thinly slice 12 ounces white button or cremini mushrooms. Mince 2 garlic cloves.

  3. Cook the mushrooms. Melt 4 tablespoons unsalted butter in a large, straight-sided skillet over medium-high heat. Add the mushrooms and cook until reduced by half, about 5 minutes. Add the garlic and cook until fragrant, about 1 minute.

  4. Make the sauce. Sprinkle 1/4 cup all-purpose flour evenly over the mushroom mixture and stir to combine. Cook until the flour is no longer dry, 1 to 2 minutes. Add 2 cups whole milk, 1 cup low-sodium chicken or vegetable broth, 1 teaspoon tamari or soy sauce, 1/2 teaspoon black pepper, and 1/2 teaspoon grated nutmeg and bring to a simmer. Simmer, stirring occasionally, until the sauce is thickened, 3 to 5 minutes.

  5. Add some of the fried onions and green beans. Remove the sauce from the heat. Add the green beans and 1/2 (6-ounce) can of the fried onions, and stir to combine. Transfer the green bean mixture to a 9x13-inch baking dish and spread into an even layer.

  6. Top and bake. Sprinkle with the remaining 1 1/2 (6-ounce) cans fried onions. Bake until golden brown and bubbling, 12 to 15 minutes.

  7. Cool before serving. Let cool for 10 minutes before serving. The sauce will thicken as it cools.

Recipe Notes

Make ahead: Assemble the casserole without the crisp onion topping and refrigerate tightly wrapped for up to 3 days. Remove from the refrigerator while the oven preheats. Uncover, top with the fried onions, and bake, it may need a few more minutes baking time.

Storage: Refrigerate leftovers in an airtight container for up to 4 days.