Set your oven to 350°F (175°C). Grease a 9×13 inch baking dish.
In a large mixing bowl, mix the hash browns with ½ cup melted butter, cream of chicken soup, sour cream, grated onion, cheddar cheese, salt, and pepper until well combined.
Spread the mixture evenly in the prepared baking dish.
Mix the crushed cornflakes with ¼ cup melted butter, then sprinkle over the potato mixture.
Bake in the preheated oven for 45-50 minutes, until the topping is golden brown and crispy.
Let the casserole cool slightly before serving to allow the layers to set.
