funeral potatoes recipe

1 package (30 ounces) frozen shredded hash browns, thawed - 1 can (10.5 ounces) condensed cream of chicken soup - 1 cup sour cream - 1/2 cup unsalted butter, melted - 1 small onion, finely chopped - 2 cups shredded cheddar cheese - 1 teaspoon salt - 1/2 teaspoon black pepper - 2 cups cornflakes cereal, crushed - 1/4 cup unsalted butter, melted (for topping)