Preheat oven to 350°F (175°C).
In a large bowl, combine hash browns, cheddar cheese, sour cream, cream of chicken soup, ½ cup melted butter, and chopped onion.
Spread mixture into a 9x13 inch baking dish.
In a separate bowl, mix together crushed cornflakes and 2 tablespoons melted butter. Sprinkle over the top of the potato mixture.
Bake in preheated oven for 45 minutes.
