Preheat oven to 350°F (175°C). Grease a 9x13-inch baking dish.
In a large bowl, mix together hash browns, 1/2 cup melted butter, soup, sour cream, onion, cheese, salt, and pepper until well combined.
Spread the mixture evenly in the prepared dish.
In a separate bowl, mix crushed cornflakes with 1/4 cup melted butter. Sprinkle evenly over the casserole.
Bake uncovered for 45-50 minutes, until hot and bubbly and the top is golden brown.