Preheat your oven to 350°F and lightly grease a 9x13-inch baking dish.
In a large bowl, mix together the thawed hash browns, melted butter, cream of chicken soup, sour cream, onion, 1 1/2 cups of the cheddar cheese, and black pepper until well combined.
Transfer the hash brown mixture to the prepared baking dish, spreading it out evenly.
Sprinkle the remaining 1/2 cup of cheddar cheese over the top of the casserole.
Bake in the preheated oven for 45 minutes, or until the casserole is hot throughout and the cheese is melted and lightly browned.
Allow the casserole to stand for a few minutes before serving.