Preheat oven to 425 degrees F.
Pour hash browns into a lightly-greased 9x13 inch baking dish. In a large bowl, combine the cheese, sour cream and soup.
In a large skillet over medium heat, combine the onion with 1 stick butter and sauté for 5 minutes. Add to the soup mixture and spread over the potatoes in the dish.
Arrange the crushed corn flakes over the potatoes and soup mixture. Melt the remaining stick of butter and pour evenly over the corn flakes.
Bake at 425 degrees F for 1 hour.