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Golden French Onion Chicken Casserole topped with melted cheese and croutons, garnished with thyme

French Onion Chicken Casserole

This French Onion Chicken Casserole is a time-saving, creamy delight featuring rotisserie chicken, delicious Gruyère cheese, and rich canned French onion soup, perfect for a quick weeknight meal!
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Prep Time 15 minutes
Cook Time 35 minutes
Resting Time 10 minutes
Total Time 1 hour
Servings: 8 servings
Course: Main Course
Cuisine: American
Ingredients Equipment Method Notes

Ingredients
  

  • 2 tablespoons unsalted butter
  • 1 1/2 cups chopped yellow onion
  • 1/2 cup chopped celery
  • 1/2 cup chopped carrot
  • 1 tablespoon finely chopped fresh garlic
  • 2 teaspoons fresh thyme leaves, plus more for garnish
  • 1 teaspoon kosher salt
  • 1 teaspoon freshly ground black pepper, plus more for garnish
  • 1 (10.5 ounce) can condensed French onion soup
  • 1 cup sour cream
  • 1 cup mayonnaise
  • 1 teaspoon Dijon mustard
  • 2 cups Gruyère cheese, shredded, divided
  • 6 cups chopped rotisserie chicken (from 1 1/2 whole rotisserie chickens)
  • 1 (5 ounce) package seasoned croutons

Equipment

  • large skillet
  • 9x13-inch baking dish
  • Cheese Grater

Method
 

  1. Gather all ingredients. Preheat the oven to 350°F (175°C). Grease a 9x13-inch baking dish.
  2. Melt butter in a skillet over medium heat. Add onions, celery, carrots, garlic, thyme, salt, and pepper. Cook, stirring, until onions are translucent, about 5-7 minutes.
  3. Stir in canned French onion soup and bring to a simmer. Allow to reduce slightly, about 2-3 minutes.
  4. Add sour cream, mayonnaise, and Dijon mustard. Stir until combined, then mix in 1 cup of Gruyère cheese. Cook until the cheese melts smoothly, about 1 minute.
  5. Fold in the rotisserie chicken until evenly coated. Transfer the mixture to the prepared baking dish.
  6. Top with croutons and sprinkle the remaining Gruyère cheese evenly over the top.
  7. Bake uncovered for 12-15 minutes, or until bubbling and golden on top. Let rest 10 minutes before serving. Garnish with additional thyme and black pepper.

Notes

Quick tip: Chop veggies like onions, carrots, and celery in advance to make assembly even faster.