Preheat oven to 350 degrees. Spray a 9x13 baking dish with non-stick spray.
Add the broccoli to a large microwave safe bowl along with ¼ cup of water. Cover tightly with plastic wrap and microwave for 5 minutes. Let stand, covered, for 5 minutes.
Carefully remove the plastic wrap and drain the liquid.
Add the chicken, cheddar, cream of chicken soup, sour cream, salt, and pepper to the bowl with the broccoli and stir well to combine.
Pour broccoli mixture into prepared baking dish.
Add 3 cups of water and the butter to a large sauce pan and bring to a boil.
Stir in the stuffing mix, cover, and remove from the heat. Let stand for 5 minutes.
Fluff stuffing with a fork and then spoon the stuffing over the casserole.
Cover the casserole dish tightly with foil and bake for 25 minutes.
Carefully remove the foil and continue baking for 15 minutes.
Serve immediately.
Video
Notes
To use frozen broccoli in place of fresh broccoli, thaw the broccoli in a bowl of warm water. Drain the water and continue with step 4.