Potato Casserole

8 cooked potatoes - shredded
1 pint sour cream
1 can cream of chicken soup
1/4 cup melted margarine
1/3 cup chopped onion
1 cup grated cheese
salt & pepper to taste

Topping:
2 cups cornflake crumbs
1/2 cup melted butter

Mix all ingredients and place into a 9x13 dish. Sprinkle with topping. Bake uncovered at 350 degrees for about 30-40 minutes until heated through.