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Best Make-Ahead Green Bean Casserole with Crispy Onions

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A make-ahead green bean casserole with a from-scratch mushroom sauce and crispy fried onions that stays crunchy even after reheating. Perfect for holidays and stress-free entertaining.

Ingredients

Scale
  • 2 pounds fresh green beans, trimmed and cut into 2-inch pieces (or 2 pounds frozen green beans, thawed and patted dry)
  • 1 tablespoon kosher salt (for blanching water)
  • 4 tablespoons unsalted butter
  • 1 pound cremini mushrooms, sliced
  • 1 medium yellow onion, finely diced
  • 4 cloves garlic, minced
  • 1/4 cup all-purpose flour
  • 2 cups whole milk, warmed
  • 1 cup heavy cream
  • 1 teaspoon kosher salt
  • 1/2 teaspoon black pepper
  • 1/4 teaspoon freshly grated nutmeg
  • 2 teaspoons soy sauce
  • 1/2 cup grated Parmesan cheese (optional)
  • 2 large yellow onions, thinly sliced into rings (for homemade fried onions)
  • 1 cup buttermilk (for homemade fried onions)
  • 1 cup all-purpose flour (for homemade fried onions)
  • 1 teaspoon kosher salt (for homemade fried onions)
  • 1/2 teaspoon black pepper (for homemade fried onions)
  • 1/2 teaspoon paprika (for homemade fried onions)
  • Vegetable or canola oil, for frying (for homemade fried onions)
  • Or 2 cups store-bought crispy fried onions
  • 1 cup shredded sharp cheddar cheese (optional)
  • Fresh parsley, chopped, for garnish

Instructions

  1. Bring a large pot of water to a rolling boil and add 1 tablespoon of kosher salt. Fill a large bowl with ice water. Add the green beans to the boiling water and cook for exactly 3 minutes (fresh) or 2 minutes (thawed frozen). Immediately transfer to the ice water bath. Let sit for 3-4 minutes until completely cool. Drain well and pat dry with a clean kitchen towel. Set aside.
  2. In a large skillet over medium-high heat, melt 2 tablespoons of butter. Add the sliced mushrooms and cook, stirring occasionally, for 6-8 minutes until they release their liquid and start to brown. Remove mushrooms from the pan and set aside.
  3. Reduce heat to medium and add the remaining 2 tablespoons of butter. Add the diced onion and cook for 4-5 minutes until softened. Add the minced garlic and cook for 30 seconds until fragrant. Sprinkle the flour over the onions and garlic, stirring constantly, and cook for 1-2 minutes until the flour turns light golden.
  4. Slowly pour in the warm milk while whisking continuously to prevent lumps. Add the heavy cream and continue whisking until the sauce thickens, about 3-4 minutes. Stir in the salt, pepper, nutmeg, soy sauce, and cooked mushrooms. If using Parmesan, add it now and stir until melted. Taste and adjust seasoning.
  5. If making homemade fried onions: Soak sliced onions in buttermilk for 10 minutes. In a shallow bowl, combine flour, salt, pepper, and paprika. Heat about 2 inches of oil in a deep pot to 350°F. Working in batches, dredge soaked onion rings in seasoned flour, shaking off excess, and fry for 2-3 minutes until golden brown. Transfer to a paper towel-lined plate and season with salt.
  6. Preheat oven to 375°F. In a large mixing bowl, combine the blanched green beans with about half of the mushroom sauce and half of the crispy fried onions (or about 1 cup of store-bought). Stir gently. Transfer to a greased 9×13 baking dish and spread into an even layer. Pour the remaining sauce over the top. If using cheddar cheese, sprinkle it over the sauce now.
  7. Cover the dish tightly with aluminum foil and refrigerate for up to 2 days. When ready to bake, remove from fridge and let sit at room temperature for 20 minutes while oven preheats.
  8. Bake covered for 25 minutes. Remove foil and bake for another 10 minutes until bubbly and golden. Sprinkle remaining crispy fried onions over the top and bake for an additional 5 minutes, uncovered, until topping is deeply golden and crunchy. Let rest for 5-10 minutes before serving.

Notes

For best results, don’t overcook the beans—3 minutes in boiling water is plenty. Warm the milk before adding to the roux to prevent lumps. Layer the onions twice: some inside the casserole and a fresh batch on top for maximum crunch. Let the casserole rest for 5-10 minutes after baking to allow the sauce to set. The casserole tastes even better on day two.

Nutrition

Keywords: green bean casserole, make-ahead, Thanksgiving, holiday side dish, crispy onions, mushroom sauce

Find it online: https://tablemira.com/best-make-ahead-green-bean-casserole-with-crispy-onions/