In a large oven-safe skillet or Dutch oven, melt 2 tablespoons of unsalted butter and 1 tablespoon of olive oil over medium-low heat. Add 2 sliced yellow onions, along with 1 tablespoon of sugar and a pinch of salt. Cook for 30–40 minutes, stirring occasionally, until the onions are golden brown and caramelized. In the final minute, add 2 minced garlic cloves for added aroma and flavor.

While the onions are caramelizing, season 2 cups of cooked shredded chicken with salt and freshly ground black pepper. In a separate skillet, heat a drizzle of olive oil over medium heat. Add the chicken and cook until golden, about 5–7 minutes. Avoid cooking it completely, as it will finish cooking in the casserole.

After the onions have caramelized, deglaze the skillet with 1 cup of beef broth, scraping up any brown bits stuck to the bottom. Stir in 1 cup of orzo pasta, 1 cup of heavy cream, and 1 teaspoon of dried thyme. Add the browned chicken and let this mixture simmer for about 5–7 minutes.

Preheat your oven to 375°F (190°C). Stir half of the 2 cups of shredded mozzarella cheese into the orzo mixture until melted, then transfer everything to the preheated oven. Top with the remaining mozzarella cheese and bake uncovered for 20–25 minutes.

Once baked, remove the Onion Chicken Orzo Casserole from the oven and let it rest for 5–10 minutes. Garnish with fresh thyme or parsley before serving.