Prep and Caramelize:

Slice 3 large yellow onions into thin half-moons. Cut chicken breasts into 1-inch pieces and season with salt, pepper, garlic powder, and thyme. Melt 2 tablespoons of butter in a large skillet over medium heat. Add the onions along with sugar and salt, and cook for 18-22 minutes until deeply golden and caramelized. Transfer the onions to a bowl and set aside.

Build the Base:

Add the remaining butter to the skillet and brown the seasoned chicken for 5-7 minutes. Add uncooked orzo and toast for 1-2 minutes. Deglaze with white wine, scraping up the browned bits. Add beef broth, Worcestershire sauce, and bay leaf, and bring to a simmer. Return the caramelized onions, and simmer for 3-4 minutes. Stir in heavy cream and remove from heat.

Add Cheese: Stir in 1 cup of Gruyère and all the mozzarella until melted. Remove the bay leaf, taste, and adjust seasoning. Sprinkle the remaining 1/2 cup of Gruyère on top.

Rest and Serve:

Let the casserole rest for 5-10 minutes before serving. Garnish with fresh parsley and thyme. Cover the casserole with foil for the first half of cooking to retain moisture. Serve hot directly from the skillet.