French Onion Chicken Casserole

A baked casserole topped with crispy fried onions in a white rectangular dish on a wooden board, surrounded by onions, utensils, and a striped cloth.

French Onion Chicken Casserole

This French Onion Chicken Casserole features slow-cooked onions, seasoned chicken, a creamy homemade sauce, and plenty of melted cheese. It has the same cozy flavor you get from French onion soup, but in a hearty baked dinner that’s great for weeknights or feeding a small crowd.

Prep Time20

Cook Time1 10

Total Time1 30

Course: Main Dish

Cuisine: American

Keyword: French Onion Chicken Casserole

Servings: servings

Calories: 857kcal

Ingredients

Onions

3 Tablespoons butter
2 large yellow onions (or 3 small) thinly sliced
2 Tablespoons water as needed

Chicken

1 teaspoon salt
1 teaspoon garlic powder
½ teaspoon oregano
¼ teaspoon pepper
1 ½ pounds chicken breasts

Casserole

1 cup milk
2 Tablespoons cornstarch
1 teaspoon Better Than Bouillon chicken base (or 1 bouillon cube or 1 teaspoon bouillon powder)
½ teaspoon salt
½ teaspoon onion powder
½ teaspoon dried parsley
1 cup sour cream
½ cup cheddar cheese freshly shredded
¾ cup mozzarella cheese freshly shredded
6 ounces French fried onions

Instructions

Preheat Oven: Preheat oven to 400 °F and grease a 9x13-inch baking dish.
Caramelize Onions: Melt 3 Tablespoons butter in a skillet over medium-low heat. Add sliced onions and cook for 25-30 minutes, stirring occasionally, until soft and golden. Add a splash of water if they look too dry. Set aside.
Prep Chicken: Mix the 1 teaspoon salt, 1 teaspoon garlic powder, ½ teaspoon oregano, and ¼ teaspoon pepper. Pat 1 ½ pounds chicken breasts dry and season both sides evenly. Place chicken in prepared baking dish.
Make Sauce: Whisk 1 cup milk and 2 Tablespoons cornstarch in a saucepan. Set over medium heat and whisk in 1 teaspoon Better Than Bouillon chicken base (or 1 bouillon cube or 1 teaspoon bouillon powder), ½ teaspoon salt, ½ teaspoon onion powder, and ½ teaspoon dried parsley. Bring to a simmer and cook for about a minute, until thickened. Remove from heat, stir in 1 cup sour cream, and let it cool for about 10 minutes.
Assemble: Spread caramelized onions evenly over chicken breasts. Stir ½ cup cheddar cheese into the sauce (cheese should soften slightly, not fully melt), then evenly pour sauce over onions and chicken. Sprinkle ¾ cup mozzarella cheese evenly on top.
Bake: Cover with foil and bake for 35-40 minutes. Remove the foil, top with 6 ounces French fried onions and bake uncovered for another 5-8 minutes, or until chicken reaches 165°F.

Notes

To Make In Advance: Assemble completely (excluding French fried onions), cover, and refrigerate 1-2 days. Add French fried onions just before baking and increase bake time by ~10 minutes if baking from cold.

Refrigerator Storage: Store leftovers in an airtight container for 3-4 days. Reheat in microwave until steaming hot, or bake covered at 350°F for about 15-20 minutes until internal temperature reaches 165°F.

Freezer Storage: This casserole doesn’t freeze well because of the dairy in the sauce. The texture changes once thawed, so it’s best to keep it refrigerated and enjoy within a few days.

Nutrition