1. Saute onion in saucepan sprayed with cooking spray.
2. Mix together soup, sour cream, cheese, onions and potatoes.
3. Spread in 2 1/2 quart baking dish sprayed with cooking spray.
4. Sprinkle top with cornflake crumbs, spritzing crumbs with cooking spray.
5. Cook at 350 for 1 to 1 1/2 hour (s).