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French Onion Broccoli Cheese Casserole

French Onion Broccoli Cheese Casserole

Caramelized onions meet tender broccoli in a creamy Gruyère-cheddar sauce, crowned with a crispy fried onion topping.
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Prep Time: 25 minutes
Cook Time: 45 minutes
Total Time: 1 hour 10 minutes
Servings: 8

Ingredients
 

Main Ingredients

  • 3 tbsp unsalted butter
  • 1 tbsp olive oil plus more for topping
  • 4 cup thinly sliced yellow onions
  • 1.25 tsp kosher salt divided
  • 0.5 tsp freshly ground black pepper
  • 1.5 tsp fresh thyme leaves or 1/2 tsp dried
  • 2 tsp minced garlic
  • 0.25 cup dry sherry or dry white wine
  • 2.5 tbsp all-purpose flour
  • 1.25 cup beef broth or vegetable broth
  • 0.75 cup whole milk or half-and-half
  • 1 tsp Dijon mustard
  • 1 tsp Worcestershire sauce
  • 1 tsp lemon juice optional
  • 0.5 cup sour cream
  • 2.5 cup shredded Gruyère cheese
  • 1 cup shredded sharp cheddar
  • 6 cup small broccoli florets
  • 0.75 cup panko breadcrumbs
  • 1.5 cup crispy fried onions
  • 1 tbsp olive oil for topping

Instructions

Preparation Steps

  • Heat oven to 375°F. Lightly grease a 9x13-inch baking dish.
  • Melt butter with 1 tbsp olive oil in a large skillet over medium-low heat.
  • Cook onions with 1 tsp salt until deep golden, 20–25 minutes, stirring occasionally.
  • Stir in thyme and garlic. Cook 1 minute until fragrant.
  • Deglaze with sherry. Simmer until almost dry, scraping up browned bits.
  • Sprinkle flour over onions. Cook 1 minute, stirring constantly.
  • Whisk in broth and milk. Simmer until thick and silky, 3–5 minutes.
  • Off heat, stir in Dijon, Worcestershire, lemon juice, and pepper. Fold in sour cream.
  • Stir in Gruyère and cheddar, reserving a small handful for topping.
  • Blanch broccoli in salted boiling water 2 minutes. Drain well and pat dry.
  • Combine broccoli with onion-cheese sauce. Spread mixture in the prepared dish.
  • Top with reserved cheese. Toss panko and fried onions with 1 tbsp oil and a pinch salt.
  • Scatter topping evenly over casserole. Bake 20–25 minutes until bubbling and golden.
  • Broil 1–2 minutes for extra color, watching closely. Rest 10 minutes before serving.

Notes

Swap half the Gruyère for Swiss or provolone, or stir in a pinch of smoked paprika. For make-ahead, assemble without the topping, cover, and refrigerate up to 24 hours; add topping and bake, adding 5–10 minutes to cook time. Serve with a crisp salad or roasted chicken.
This recipe is an original creation inspired by classic French Onion Broccoli Cheese Casserole flavors. All ingredient ratios and instructions are independently developed.