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Best Creamy Make-Ahead Green Bean Casserole with Crispy Onions

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This creamy make-ahead green bean casserole with crispy onions is the ultimate holiday side dish. Made from scratch with fresh green beans, a velvety mushroom sauce, and homemade crispy onions, it can be assembled a day ahead for stress-free entertaining.

Ingredients

Scale
  • 2 pounds fresh green beans, trimmed and cut into 2-inch pieces
  • 4 tablespoons unsalted butter
  • 8 ounces cremini mushrooms, sliced
  • 1 medium yellow onion, finely diced
  • 3 cloves garlic, minced
  • 1/4 cup all-purpose flour
  • 1 1/2 cups whole milk
  • 1/2 cup heavy cream
  • 1 cup low-sodium chicken or vegetable broth
  • 1/2 cup sour cream, at room temperature
  • 1/4 cup grated Parmesan cheese (optional)
  • 1 teaspoon salt
  • 1/2 teaspoon black pepper, freshly ground
  • 1/2 teaspoon dried thyme
  • Pinch of nutmeg (freshly grated if possible)
  • 2 large yellow onions, thinly sliced into rings
  • 1 cup buttermilk
  • 1 cup all-purpose flour
  • 1/2 cup panko breadcrumbs
  • 1 teaspoon salt
  • 1 teaspoon paprika
  • 1/2 teaspoon garlic powder
  • Vegetable or canola oil for frying (about 2 cups)

Instructions

  1. Blanch the green beans: Bring a large pot of salted water to a rolling boil. Add the trimmed green beans and cook for exactly 3 minutes. Drain and transfer to a bowl of ice water to stop the cooking. Let sit for 2 minutes, then drain well and pat dry. Set aside.
  2. Make the creamy sauce: In a large skillet, melt the butter over medium heat. Add the sliced mushrooms and cook, stirring occasionally, for 6-8 minutes until they release their liquid and start to brown. Add the diced onion and cook for 3 minutes until softened. Stir in the minced garlic and cook for 30 seconds until fragrant.
  3. Sprinkle the flour over the mushroom mixture and stir constantly for 1 minute. Slowly pour in the milk, heavy cream, and broth while whisking continuously. Keep whisking until the sauce thickens, about 3-4 minutes. Stir in the sour cream, Parmesan (if using), salt, pepper, thyme, and nutmeg. Taste and adjust seasoning.
  4. Make the crispy onions: Soak the sliced onions in buttermilk for 10 minutes. In a shallow bowl, whisk together the flour, panko, salt, paprika, and garlic powder. Heat about 2 inches of oil in a deep pot to 350°F (175°C). Working in batches, dredge the soaked onion rings in the flour mixture, shaking off excess. Fry for 2-3 minutes, turning once, until deep golden brown. Drain on paper towels and sprinkle with salt while hot.
  5. Assemble the casserole: Preheat oven to 375°F (190°C). In a large bowl, combine the blanched green beans with the creamy mushroom sauce. Gently fold until every bean is coated. Transfer to a greased 9×13-inch baking dish and spread evenly. If making ahead, cover tightly with foil and refrigerate for up to 24 hours.
  6. Bake and top: When ready to bake, remove casserole from fridge and let sit on counter for 20 minutes. Bake covered with foil for 25 minutes (30 if cold from fridge). Remove foil, sprinkle crispy onions evenly on top, and bake uncovered for 10-15 minutes until topping is golden and casserole is bubbly. Let rest 5 minutes before serving.

Notes

For make-ahead, assemble casserole without crispy onions up to 24 hours in advance. Fry onions fresh on serving day for best crunch. If sauce is lumpy, strain through a fine-mesh sieve or use an immersion blender. For gluten-free, use a 1:1 gluten-free flour blend and gluten-free panko. For dairy-free, use plant-based butter, unsweetened oat milk or cashew cream, and dairy-free sour cream.

Nutrition

Keywords: green bean casserole, make-ahead, creamy, crispy onions, holiday side dish, Thanksgiving, from scratch

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