Preheat oven to 350°F (175°C) and grease a casserole dish.
In a large bowl combine shredded chicken, stuffing mix, onion, and celery.
In another bowl mix cream of chicken soup, chicken broth, sour cream, melted butter, poultry seasoning, and black pepper.
Pour the soup mixture over the chicken mixture and stir until evenly combined.
Spread the mixture evenly in the prepared casserole dish.
Cover with foil and bake for 25 minutes.
Remove foil and bake another 15 minutes until the top becomes lightly golden.
Let the casserole rest for 5 minutes before serving.