01 -
In a large oven-safe skillet over medium-low heat, melt butter with olive oil. Add sliced onions and cook slowly, stirring frequently, until deeply golden and caramelized, about 35 minutes. Stir in minced garlic and cook for an additional minute.
02 -
Season chicken pieces with half of the salt and black pepper. Brown the chicken in a separate skillet over medium-high heat until golden on both sides, about 3 minutes per side. Remove and set aside; chicken will finish cooking in the oven.
03 -
Deglaze the caramelized onions with beef broth, scraping up browned bits. Stir in orzo, heavy cream, fresh thyme, browned chicken, and remaining salt and pepper. Simmer for 5 to 7 minutes until orzo begins to absorb liquid but retains slight firmness.
04 -
Stir half of the Gruyère cheese into the mixture. Sprinkle the remaining cheese evenly on top. Transfer skillet to a preheated oven at 375°F and bake uncovered for 20 to 25 minutes until the top is golden and bubbly.
05 -
Allow the casserole to rest for 5 to 10 minutes before serving to let it thicken. Garnish with additional thyme or chopped parsley, if desired.