In a large bowl, combine shredded hashbrowns, sour cream, cream of chicken soup, cheddar cheese, garlic powder, onion powder, and black pepper. Mix until well-combined.
Melt the butter and toss with cornflakes.
In a greased 9x13 pan, pour the hashbrown mixture and spread it even. Top with buttered corn flakes and bake for 45-50 minutes covered with foil.