01 -
In a large oven-safe skillet or Dutch oven, heat butter and olive oil over medium-low heat. Add thinly sliced onions and cook slowly, stirring frequently, until deeply golden and caramelized, approximately 30 to 40 minutes. Add minced garlic and cook for 1 additional minute.
02 -
While onions cook, season chicken with salt and pepper. In a separate skillet or after temporarily removing onions, brown chicken pieces over medium heat until golden on both sides but not fully cooked.
03 -
Add beef broth to the caramelized onions, scraping up any browned bits. Stir in orzo pasta, heavy cream, fresh thyme, and browned chicken. Simmer gently for 5 to 7 minutes until orzo absorbs liquid but remains slightly firm.
04 -
Incorporate half of the Gruyère cheese into the mixture. Top with remaining cheese, then transfer skillet to a preheated oven at 190°C. Bake uncovered for 20 to 25 minutes, until the surface is golden and bubbling.
05 -
Allow the casserole to rest for 5 to 10 minutes to thicken before serving. Garnish with additional thyme or chopped parsley if desired.