Preheat the oven to 375 degrees and spray a 9/13 casserole dish with cooking spray. Set aside.

Add ¼ cup butter to the water in a saucepan, then bring to a boil.

Add in the stuffing mix, stir, then remove from heat and cover the pot with a lid. Let it sit for about 5 minutes until the water is absorbed, then fluff with a fork.

Cook the onion and celery in the remaining tablespoon of butter until translucent, about 8 minutes.

In a separate bowl, mix together both soups and the sour cream

Layer the casserole. Lay the chicken evenly over the bottom of the dish. Top with the cooked vegetables and season with salt and pepper. Pour over the soup mixture and then top with the stuffing.

Bake for about an hour, or until bubbling and lightly browned.