Step 1: Preheat the Oven

1. Preheat your oven to 375°F (190°C).
2. Grease a 9×13-inch baking dish with butter or nonstick spray.

Step 2: Prepare the Chicken

1. Season the chicken breasts with garlic powder, onion powder, salt, and pepper.
2. Arrange the chicken in a single layer in the prepared baking dish.

Step 3: Make the Stuffing Mixture

1. In a medium bowl, combine the stuffing mix, chicken broth, and melted butter. Stir until the stuffing is moist but not overly soggy.
2. Set aside to allow the stuffing to absorb the liquid.

Step 4: Mix the Creamy Sauce

1. In another bowl, whisk together the cream of chicken soup, sour cream, and milk until smooth.
2. Pour this mixture evenly over the chicken breasts in the baking dish.

Step 5: Assemble the Casserole

1. Spread the prepared stuffing mixture over the chicken and sauce layers.
2. Sprinkle shredded cheddar cheese on top if desired.

Step 6: Bake the Casserole

1. Cover the dish with aluminum foil and bake for 25 minutes.
2. Remove the foil and bake for an additional 15-20 minutes, or until the chicken reaches an internal temperature of 165°F (74°C) and the stuffing is golden brown.

Step 7: Rest and Serve

1. Let the casserole rest for 5-10 minutes after removing it from the oven. This allows the flavors to meld and makes it easier to serve.
2. Serve hot, garnished with fresh parsley if desired.