Stir in the cream of mushroom/chicken soup, sour cream or softened cream cheese, and chicken broth. Whisk until smooth. If using cream cheese, ensure it’s fully melted and incorporated.
Gradually add 2 cups of shredded cheddar cheese to the sauce, stirring until melted and smooth. Season with salt and black pepper to taste. For a spicy kick, add red pepper flakes or diced jalapeño.
In a large bowl, combine the cooked al dente spaghetti with the cooked chicken. Pour the creamy cheese sauce over the spaghetti and chicken mixture and stir gently until everything is well coated.
Transfer the mixture into a 9×13 inch baking dish. Ensure even distribution. Sprinkle the remaining shredded cheese generously over the top of the casserole.
Bake in the preheated oven for 25-35 minutes, or until the sauce is bubbly around the edges and the cheese on top is melted and golden brown. If the top browns too quickly, you can loosely cover it with foil.
Remove from the oven and let the casserole rest for 10-15 minutes before serving. This allows the sauce to set and makes for easier, cleaner portions. Garnish with fresh parsley or green onions if desired.
Serve warm with your favorite side dishes, such as a green salad or garlic bread.
