Preheat your oven to 375°F (190°C) and grease a 9×13-inch baking dish with butter or nonstick spray.

In a large skillet, melt a tablespoon of butter over medium heat. Add diced onions and cook for about 4–5 minutes until translucent. Stir in minced garlic and sauté for another 30 seconds until fragrant.

In a large bowl, combine your cooked chicken, fluffy rice, chicken broth, sautéed onions, and vibrant carrots. If using, add a dollop of sour cream or cream cheese for enhanced creaminess.

Carefully pour the chicken and rice mixture into the prepared baking dish, leveling it out with a spatula.

Sprinkle shredded cheddar cheese over the top of the casserole. Cover the dish with aluminum foil.

Bake covered in the preheated oven for 45–50 minutes. Remove the foil during the last 5–10 minutes if you like a crispy top.

Let your casserole rest for 5–10 minutes before serving. Garnish with fresh parsley or chives.