Preheat oven to 425 degrees F (220 degrees C).
Pour the hash browns into a lightly greased 9×13 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 saute for 5 minutes. Add this to the soup mixture and spread this over the potatoes in the dish.
Next, arrange the crushed corn flakes over all in the dish. Melt the remaining stick of butter and pour this evenly over the corn flakes.
Bake at 425 degrees F (220 degrees C) for 1 hour.