Description
This French Onion Broccoli Cheese Casserole is a comforting and flavorful baked dish combining tender blanched broccoli, deeply caramelized onions, and a rich, creamy cheese sauce made with Gruyère, sharp cheddar, and Parmesan. Topped with a crispy mixture of French fried onions and panko breadcrumbs, this casserole offers a perfect balance of creamy, savory, and crunchy textures. Ideal as a hearty side dish or a vegetarian main, it embraces the classic taste of French onion soup flavors in a unique vegetable casserole format.
Ingredients
Scale
Vegetables and Aromatics
- 4 cups fresh broccoli florets (about 2 small heads), cut into bite-size pieces
- 1 large yellow onion, thinly sliced
- 2 cloves garlic, minced
- 1 tsp fresh thyme leaves or 1/2 tsp dried thyme
For Caramelizing Onions
- 2 tbsp unsalted butter
- 1 tbsp olive oil
- 1 tsp sugar (optional, to help caramelize onions)
- 1/2 tsp salt
- 1/4 tsp black pepper
For Cheese Sauce
- 2 tbsp unsalted butter
- 2 tbsp all-purpose flour
- 1 1/2 cups low-sodium chicken broth or vegetable broth
- 1 cup whole milk or half-and-half, at room temperature
- 1 tbsp Dijon mustard
- 1 tsp Worcestershire sauce (optional, but recommended)
- 1/2 tsp kosher salt
- 1/4 tsp black pepper
- 1/4 tsp smoked paprika or sweet paprika
- 1 1/2 cups shredded Gruyère cheese, divided
- 1 1/2 cups shredded sharp cheddar cheese, divided
- 1/2 cup finely grated Parmesan cheese, divided
For Casserole Mixture and Topping
- 6 cups lightly crushed French fried onions, divided (about a 6 oz can)
- 1 cup panko breadcrumbs
- 2 tbsp melted butter (for topping)
- Cooking spray or a little butter for greasing the baking dish
Instructions
- Prepare the baking dish: Lightly grease a 9×13-inch baking dish with cooking spray or butter and set aside. Preheat your oven to 375°F (190°C).
- Blanch the broccoli: Bring a large pot of salted water to a boil. Add the broccoli florets and cook for 2 to 3 minutes until they are bright green and just crisp-tender. Drain immediately and transfer to a bowl of ice water to stop cooking and preserve color. After a few minutes, drain well and pat dry with paper towels.
- Caramelize the onions: Heat 2 tbsp butter and 1 tbsp olive oil in a large skillet over medium heat. Add the thinly sliced onions, sprinkle with 1/2 tsp salt and optional 1 tsp sugar, and cook, stirring occasionally, for 20 to 30 minutes until deep golden brown and caramelized, adjusting heat as needed. In the last few minutes, add minced garlic and thyme and cook until fragrant. Remove from heat.
- Make the French onion cheese sauce: In a medium saucepan over medium heat, melt 2 tbsp butter, then whisk in 2 tbsp flour and cook 1-2 minutes until a smooth roux forms. Gradually whisk in chicken or vegetable broth, then milk or half-and-half. Stir in Dijon mustard, Worcestershire sauce (if using), salt, pepper, and paprika. Simmer gently 3 to 5 minutes until thickened. Reduce heat to low, add 1 cup Gruyère, 1 cup cheddar, and 1/4 cup Parmesan, stirring until melted and smooth. Adjust seasoning if needed, then remove from heat.
- Combine broccoli, onions, and sauce: In a large bowl, toss the blanched and dried broccoli with the caramelized onion mixture. Pour the warm cheese sauce over and gently fold until all is well coated.
- Add French fried onions inside the casserole: Fold 2 cups of the crushed French fried onions into the broccoli-cheese mixture for added flavor and texture throughout the casserole.
- Assemble the casserole: Transfer the mixture evenly to the prepared baking dish. Sprinkle the top with the remaining 1/2 cup Gruyère, 1/2 cup cheddar, and 1/4 cup Parmesan cheeses.
- Make the crispy topping: In a medium bowl, combine the remaining 4 cups crushed French fried onions with 1 cup panko breadcrumbs. Drizzle with 2 tbsp melted butter and toss until evenly coated. Sprinkle this topping evenly over the cheese layer.
- Bake the casserole: Bake in the preheated 375°F (190°C) oven for 20 to 25 minutes until the topping is deep golden and crispy, the cheese is melted, and edges bubble. If topping browns too quickly, tent with foil during the last 5 to 10 minutes.
- Rest and serve: Remove from oven and let rest for 10 minutes to set. Serve warm as a hearty side dish or main course alongside a simple salad or crusty bread.
Notes
- Blanching broccoli helps retain vibrant color and crisp-tender texture.
- Caramelizing onions slowly enhances their sweetness and adds depth of flavor.
- Worcestershire sauce in the cheese sauce is optional but adds an umami boost.
- Using a mix of Gruyère, cheddar, and Parmesan creates a complex cheese flavor and smooth sauce.
- Crushing French fried onions inside and on top provides texture throughout the casserole.
- Letting the casserole rest before serving helps it hold its shape when scooped.
- This dish can be made vegetarian if vegetable broth and vegetarian Worcestershire sauce are used.
- Use low-sodium broth to control salt levels.
- If you prefer, half-and-half yields a richer cheese sauce than whole milk.
