Caramelize the Onions:
In a large skillet, heat butter and olive oil over medium heat. Add sliced onions and cook slowly, stirring often, until golden brown and caramelized — about 20–25 minutes.
Cook the Chicken:
Push onions to the side of the skillet. Season chicken with salt, pepper, garlic powder, and thyme. Sear each side for 3–4 minutes until golden brown.
Make the Sauce:
Add beef broth and heavy cream to the pan. Stir well and simmer for 5–7 minutes until the sauce thickens slightly.
Add the Cheese:
Sprinkle mozzarella and Parmesan cheese over the chicken. Cover the skillet until the cheese melts into a rich, creamy sauce.
Serve:
Garnish with fresh parsley. Serve hot over rice, mashed potatoes, or noodles for a comforting french onion chicken and rice style meal.