Preheat oven to 350 degrees F (175 degrees C).
In a large bowl, combine hash browns, 1/2 cup melted butter, cream of chicken soup, sour cream, chopped onion, Cheddar cheese, salt and pepper. Place mixture in a 3 quart casserole dish.
In a medium saucepan over medium heat, saute cornflakes in 1/4 cup melted butter, and sprinkle the mixture over the top of the casserole.
Bake covered in preheated oven for 40 minutes.