Preheat your oven to 350°F. Lightly grease your baking dish with butter or oil so the casserole does not stick and cleaning up later becomes much easier.

If your chicken is not cooked yet, boil or bake it until tender and fully done. Let it cool slightly, then shred or cut into small bite sized pieces.

In a large bowl, combine cream of chicken soup, sour cream, milk, and chicken broth. Stir everything well until the mixture becomes smooth, creamy, and free of lumps.

Add garlic powder, salt, and black pepper into the creamy mixture. Stir again gently so the seasoning spreads evenly and enhances the overall flavor of the casserole.

Add the cooked chicken into the bowl. If you are using celery and onion, mix them in now. Stir everything until well combined and evenly coated with the creamy mixture.

In another bowl, mix the stuffing mix with melted butter. Add a small amount of warm water if needed so the stuffing softens slightly and becomes easy to spread.

Spread the chicken mixture evenly into your prepared baking dish. Then gently add the stuffing mixture on top, creating a thick and even layer across the surface.

Place the dish in the oven and bake for about 40 minutes. The top should turn golden brown and the casserole should be bubbling around the edges.

Remove the casserole from the oven and let it rest for about five minutes before serving. This helps the layers settle and makes it easier to scoop and serve neatly.