Creamy French Onion Chicken Casserole

Start by preheating your oven to 400°F (200°C). While the oven is warming up, season the chicken breasts with salt and pepper - something I strongly recommend to give the chicken extra flavor.

Heat oil in a cast-iron skillet or oven-safe pan over medium heat. Add the chicken and cook for about 5-6 minutes on each side, or until they are evenly browned. I've found that ensuring an even browning on both sides is key to the chicken's flavor and juiciness. Remove the chicken and set aside.

In the same pan, add the sliced onions. Let them cook on medium heat for 10-15 minutes, or until they become caramelized and tender. This process can't be rushed; properly caramelizing the onions brings out their natural sweetness, an essential aspect of this decadent dish.

Next, stir in the garlic and cook for another minute. Add the beef broth, making sure to scrape any bits off the pan. It's those bits that give the dish a robust flavor. Bring it to a simmer. Add the cream and thyme, continuing to simmer until the sauce thickens. Now, add salt and pepper according to your preference.

Place the chicken back into the pan and sprinkle the tops with gruyere cheese. Transfer the pan to the preheated oven, and bake for 15 minutes, or until the cheese is bubbly and the chicken is cooked through. Here's a useful tip: always check the doneness of the chicken with a meat thermometer—an internal temperature of 165°F (74°C) means your chicken is perfectly cooked.

Finally, garnish with some freshly chopped parsley, and your creamy French onion chicken is ready to be served.