Mince the onion.

Sauté the minced onion in butter until softened.

Thaw the frozen hashbrowns.

In a large bowl, combine the sautéed onion, thawed hashbrowns, cream of chicken soup, grated cheese, and sour cream.

Mix all ingredients thoroughly.

Butter a rectangular baking dish.

Pour the hashbrown mixture into the buttered dish.

Crush the corn flakes and sprinkle them evenly over the top of the casserole.

Bake at 350 degrees Fahrenheit (175 degrees Celsius) for 45 minutes, or until golden brown and bubbly.

Let cool slightly before serving.

Serve hot.