1. Place the boneless, skinless chicken breast meat into a large saucepan with lightly salted water. Allow the water to come to a boil and cook the chicken until it’s thoroughly done, about 30 minutes. Once cooked, set the chicken aside and reserve the cooking broth.
2. Cut the cooked chicken into bite-sized pieces and distribute them evenly in a 9×13-inch baking dish.
3. Preheat your oven to 350 degrees F (175 degrees C).
4. In a medium-sized bowl, combine the condensed cream of chicken soup and the condensed cream of celery soup.
5. Using one of the empty soup cans, measure out 10 ½ fluid ounces of milk. Mix the milk with the condensed soups until well blended. Pour this mixture evenly over the chicken in the baking dish.
6. In a separate small bowl, mix the seasoned cornbread stuffing mix with the chicken broth until the stuffing is moistened.
7. If using, add the finely diced onion and the chopped celery to the stuffing and broth mixture. Thoroughly combine all the ingredients.
8. Spoon the stuffing mixture uniformly over the chicken and soup mixture in the baking dish.
9. Place the baking dish into the preheated oven and bake for approximately 45 minutes, or until the casserole is heated throughout and the top has turned a golden brown.
10. After baking, remove the casserole from the oven and allow it to cool slightly before serving.
