Preheat oven to 350 degrees.
Grease or spray a 9×13″ pan or baking dish; set aside.
In a large bowl, combine thawed hash browns with 1/2 cup of the melted butter, pepper, salt, and chopped onion, blending well.
Add in the soup and sour cream, then the cheddar cheese, mixing everything well.
Spread mixture evenly into a 9×13″ baking dish.
Mix remaining 1/4 cup melted butter and the crushed corn flakes together and sprinkle over top of casserole.
Bake at 350 degrees, uncovered, for 50 to 60 minutes. Serve hot.