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French Onion Chicken Casserole with Gruyere Cheese

French onion chicken casserole layers browned chicken and deeply golden, soft onions in a creamy beef-broth sauce. Baguette slices and shredded Gruyere bake on top until the bread is toasted and the sauce is bubbling.
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Prep Time 20 minutes
Cook Time 1 hour 5 minutes
resting 5 minutes
Total Time 1 hour 30 minutes
Servings: 6 servings
Course: Dinner
Cuisine: French
Calories: 570
Ingredients Equipment Method Notes

Ingredients
  

For the casserole
  • 4 tbsp unsalted butter divided
  • 2 lb chicken breasts boneless, skinless; cut into 1-inch pieces
  • 1 tsp kosher salt
  • 0.5 tsp black pepper
  • 1 tbsp olive oil
  • 3 yellow onions large; thinly sliced
  • 1 tbsp fresh thyme leaves
  • 2 tbsp all-purpose flour
  • 1.5 cup low-sodium beef broth
  • 1 tsp Worcestershire sauce
  • 0.5 cup heavy cream
For the topping
  • 12 baguette slices 1/2-inch-thick
  • 6 oz Gruyere cheese shredded

Equipment

  • 1 9x13-inch baking dish
  • 1 12-inch skillet

Method
 

Make the chicken and onion filling
  1. Heat the oven to 375°F.
  2. Grease a 9x13-inch baking dish with 1 tablespoon of the butter.
  3. Season the chicken pieces with the salt and black pepper.
  4. Heat the olive oil in a 12-inch skillet over medium-high heat.
  5. Brown the chicken in batches for 2 to 3 minutes per batch, turning once; transfer it to a plate without cooking it through.
  6. Melt the remaining 3 tablespoons butter in the skillet over medium heat.
  7. Add the onions and thyme and cook for 25 to 30 minutes, stirring often, until the onions are deeply golden and very soft.
  8. Stir in the flour and cook for 1 minute.
  9. Gradually stir in the beef broth and Worcestershire sauce, scraping up browned bits, and simmer for 2 to 3 minutes until slightly thickened.
  10. Stir in the heavy cream.
Top and bake
  1. Return the chicken and any accumulated juices to the skillet and stir to coat.
  2. Transfer the mixture to the prepared baking dish.
  3. Arrange the baguette slices on top.
  4. Sprinkle with the Gruyere.
  5. Bake uncovered for 20 to 25 minutes, until the sauce is bubbling, the bread is toasted, and the thickest chicken pieces reach 165°F.
  6. Rest for 5 minutes before serving.

Notes

For the deepest onion flavor, cook them until deeply golden and very soft. Refrigerate leftovers for 3 to 4 days; freezing is possible, though the baguette topping may soften. For a gluten-free variation, use gluten-free flour and bread.