Grease a 9 x 13-inch baking dish. Preheat the oven to 325 degrees.
In a large mixing bowl, combine the cream of chicken soup, sour cream, cheddar cheese, and onion. Mix well. Season to taste with salt and pepper. Stir in potatoes. Spoon this mixture into the prepared baking dish.
In a small mixing bowl, combine crushed cornflakes and melted butter. Sprinkle over the potato mixture.
Bake for 2 hours at 325 degrees.
Note: the dish can be frozen prior to baking. Simply wrap well and freeze for 4 to 6 weeks. To serve: bake according to directions.If you prefer saucier potatoes, use 2 more cups of cream of chicken soup.