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French Onion Broccoli Cheese Casserole

French Onion Broccoli & Cheese Casserole

Ultra-creamy French onion broccoli cheese casserole with caramelized onions, Gruyère, cheddar, and crispy fried onions. No canned soup, make-ahead, freezer-friendly.
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Course: Side Dish
Cuisine: American
Keyword: broccoli casserole, cheesy side, french onion, gruyere
Prep Time: 20 minutes
Cook Time: 35 minutes
Total Time: 55 minutes
Servings: 8 servings

Equipment

  • Large skillet
  • Saucepan or sauté pan
  • 9x13-inch baking dish
  • Whisk
  • Mixing bowl

Ingredients
  

Ingredients

  • 1 tablespoon olive oil
  • 2 tablespoons unsalted butter for onions
  • 2 large yellow onions, thinly sliced
  • 1/2 teaspoon granulated sugar
  • 1 teaspoon kosher salt divided
  • 2 garlic cloves, minced
  • 1/2 teaspoon dried thyme
  • 2 tablespoons unsalted butter for roux
  • 2 tablespoons all-purpose flour
  • 1 cup low-sodium beef broth
  • 1 cup whole milk
  • 4 cups broccoli florets blanched and well-drained
  • 6 ounces Gruyère cheese, shredded
  • 1 cup sharp cheddar cheese, shredded divided
  • 1/2 teaspoon ground black pepper
  • 1 cup panko breadcrumbs
  • 2 tablespoons unsalted butter, melted for topping
  • 1 tablespoon fresh parsley, chopped optional

Instructions

  • Heat oven to 375°F. Grease a 9x13-inch baking dish.
  • Caramelize the onions: Warm the olive oil and 2 tablespoons butter in a large skillet over medium-low heat. Add the sliced onions, 1/2 teaspoon of the salt, and the sugar. Cook, stirring occasionally, until deeply golden and jammy, 20–25 minutes. Stir in the garlic and thyme for 1 minute. Remove from heat.
  • Blanch the broccoli: Cook florets in boiling salted water for 2 minutes until bright green and crisp-tender. Drain well and pat dry so the sauce isn’t watery.
  • Make the cheese sauce: In a saucepan, melt 2 tablespoons butter over medium heat. Whisk in flour and cook 1 minute. Slowly whisk in beef broth, then milk, and simmer, whisking, until thickened, 3–4 minutes.
  • Off heat, stir in the Gruyère and half of the cheddar until smooth. Season with the remaining 1/2 teaspoon salt and the black pepper.
  • Assemble: In the prepared dish, combine the blanched broccoli, caramelized onions, and cheese sauce. Sprinkle with the remaining cheddar.
  • Topping: Mix panko with melted butter (and parsley, if using). Scatter evenly over the casserole.
  • Bake 18–22 minutes, until bubbling and the top is golden. Let rest 5–10 minutes before serving.

Notes

Shortcuts: Use frozen broccoli; thaw and drain well before mixing. Swap vegetable broth for beef if you prefer. Cheese swaps: Swiss or Jarlsberg work for Gruyère; Monterey Jack can replace cheddar. Topping ideas: French-fried onions are a great alternative to panko. Make-ahead: Assemble (without topping) up to 1 day ahead, refrigerate, then add topping and bake, adding 5–10 minutes if cold. Storage: Refrigerate leftovers up to 4 days; reheat covered at 350°F.
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