French Onion Broccoli Cheese Casserole
A rich and comforting French Onion Broccoli Cheese Casserole made with caramelized onions, crisp broccoli, a creamy Gruyère–cheddar sauce, and a buttery panko topping. Perfect for holidays, potlucks, or cozy weeknight dinners.
8 Servings
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
Prepare the baking dish.
- Preheat the oven to 375°F. Grease a 9×13-inch baking dish and set aside.
Caramelize the onions.
- In a large skillet, heat the olive oil and 2 tablespoons butter over medium-low heat. Add the sliced onions, 1/2 teaspoon of the kosher salt, and the granulated sugar. Cook, stirring occasionally, until the onions become deeply golden and caramelized, approximately 20–25 minutes. Add the garlic and thyme; cook for an additional 1 minute. Remove from heat.
Blanch the broccoli.
- Bring a pot of salted water to a boil. Add the broccoli florets and cook for 2 minutes, until bright green and crisp-tender. Drain thoroughly and pat dry to prevent excess moisture in the casserole.
Prepare the cheese sauce.
- In a medium saucepan, melt 2 tablespoons butter over medium heat. Add the flour and cook, whisking continuously, for 1 minute to form a roux. Slowly whisk in the beef broth, followed by the milk. Simmer, whisking frequently, until the sauce thickens, 3–4 minutes. Remove from heat and stir in the Gruyère and half of the cheddar cheese until smooth. Season with the remaining 1/2 teaspoon salt and the black pepper.
Assemble the casserole.
- In the prepared baking dish, combine the blanched broccoli, caramelized onions, and cheese sauce. Stir gently to distribute the ingredients evenly. Sprinkle the remaining cheddar cheese across the top.
Prepare the breadcrumb topping.
- In a small bowl, combine the panko breadcrumbs with the melted butter (and parsley, if using). Distribute the mixture evenly over the surface of the casserole.
Bake.
- Bake for 18–22 minutes, or until the casserole is bubbling and the topping is golden brown. Allow the casserole to rest for 5–10 minutes before serving.
Notes
To make this French Onion Broccoli Cheese Casserole gluten-free:
- Use gluten-free all-purpose flour when preparing the roux.
- Select gluten-free panko breadcrumbs for the topping.
- Ensure the beef broth is labeled gluten-free.
- All other listed ingredients are generally gluten-free but verify packaging to be certain.