The chicken is the star of this dish, and you want to ensure it’s tender and flavorful. Start by seasoning your boneless, skinless chicken breasts or chicken thighs with a pinch of salt, pepper, and a sprinkle of garlic powder. Heat some olive oil in a skillet over medium-high heat, and brown the chicken on both sides for about 3-4 minutes each. Browning the chicken before adding it to the casserole adds an extra layer of flavor that will make the dish even more delicious.

Caramelized onions are the key to bringing that sweet, savory depth to the casserole. Thinly slice the yellow onions and cook them gently in a skillet with a touch of olive oil over low heat. Stir occasionally, letting the onions soften and slowly turn golden brown. This step is crucial, as it releases the natural sugars in the onions, creating that irresistible caramelized flavor. It usually takes about 20-25 minutes, but the result is worth every minute.

With the chicken and onions prepared, you're ready to assemble the casserole. In a baking dish, layer the browned chicken at the bottom, then spread the caramelized onions on top. In another bowl, combine the French onion soup mix with heavy cream and chicken broth. Drizzle the creamy mixture over the chicken and onions. Top it off with a generous amount of shredded cheese a combination of Gruyère and Swiss is perfect for achieving a rich, melty topping.

Cover the casserole with foil and bake it in the oven at 375°F for about 25-30 minutes. Take off the foil during the final 10 minutes to let the cheese brown and bubble. The result? A golden, cheesy, and creamy casserole that will have everyone coming back for seconds.