Preheat the oven to 350°F
Grease a 9×13-inch baking dish
In a large bowl, combine 1 package frozen hash browns, 1 can cream of chicken soup, 2 cups shredded cheddar cheese, 1 cup sour cream, 1/2 cup melted butter, 1/2 cup chopped onion, 1 teaspoon salt, and 1/2 teaspoon black pepper
Mix until well combined
Spread the mixture evenly into the prepared baking dish
In a separate bowl, mix 2 cups crushed cornflakes with 1/4 cup melted butter
Sprinkle the cornflake mixture evenly over the top
Bake for 45 to 55 minutes, until hot and bubbly and the top is golden brown
Let cool slightly before serving