Preheat your oven to 375°F and lightly grease a 9x13-inch baking dish.
In a large mixing bowl, combine the thawed hash browns, melted butter, cream of chicken soup, sour cream, chopped onion, 1 1/2 cups of the shredded cheddar cheese, salt, and pepper.
Spread the hash brown mixture evenly into the prepared baking dish.
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 golden brown on top and heated through.