Preheat oven to 400 degrees Fahrenheit.
In a large mixing bowl, combine ingredients in this order: shredded hash browns, 1 cup of shredded sharp cheddar, sour cream, cream of mushroom soup, salt and pepper.
Add 1/2 cup of melted butter and mix thoroughly, again.
Spread evenly into a 9 x 13-inch casserole dish. Top with 3 cups of shredded cheddar cheese.
Bake covered with aluminum foil for 35 minutes.
Remove foil and bake uncovered for an additional 10-15 to fully melt cheese on top.