Preheat the oven to 375F.
In a small saucepan, bring the water and 4 tablespoons of butter to a boil. Turn off the heat and add the stuffing mix. Put the lid on and let it rest for a couple of minutes. Fluff with a fork to make it easier to sprinkle on top of the casserole.
Heat ½ tbsp of butter in a large skillet and saute the onions, celery, and carrots. When chopping the veggies, try to make everything the same size. That way, you make sure there is a bit of each in every bite, and they cook evenly. Saute them for about 4-5 minutes or until they are soft.
While the veggies are cooking, whisk together the undiluted condensed cream of chicken soup, mushroom soups, and sour cream until they are well combined. Do not add any liquid to this mixture.
Spray a 9 x 13-inch casserole dish with cooking spray. It’s time to assemble the casserole, and we will do it in layers. The first layer is the shredded chicken. Layer the chicken on the bottom of the casserole dish.
Next comes the veggie layer. Place the sauteed veggies evenly on top of the shredded chicken. It is important to distribute the veggies evenly, so every bite has veggies on it.
Third layer is the soup mixture. Pour it evenly on top of the veggies. Remember not to add any water or liquid to the soups. They have the right amount of moisture for the casserole.
Time for the top layer. Sprinkle the Stove Top stuffing mixture on top of the soup mixture. Try to distribute the stuffing evenly over the whole casserole.
Bake for 45-55 minutes or until the casserole is bubbly and the stuffing is browned and crunchy.