In a large skillet or Dutch oven, melt 3 tablespoons of unsalted butter with 2 tablespoons of olive oil over medium-low heat. Add 3 large sliced yellow onions along with 1 teaspoon of sugar and a pinch of salt. Cook for 30–40 minutes, until the onions are deeply caramelized.

While the onions are caramelizing, heat another skillet over medium heat. Season about 2 cups of cooked shredded chicken with salt and pepper. Brown the chicken for about 5–7 minutes until slightly golden.

Once the onions are caramelized, pour in 1 cup of low-sodium chicken broth to deglaze the pan. Stir in 1.5 cups of orzo pasta, 3/4 cup of heavy cream, 1 tablespoon of dried thyme, and the cooked chicken. Let it simmer for 5–7 minutes.

Preheat your oven to 375°F (190°C). Remove the skillet from heat and stir in 1.5 cups of shredded mozzarella cheese until melted. Transfer to a greased baking dish and top with remaining mozzarella and 1/2 cup of grated Parmesan cheese. Bake uncovered for 20–25 minutes.

Allow the casserole to rest for 5–10 minutes before serving. Garnish with extra thyme or chopped parsley if desired.