Hearty Potato Soup

In a large stockpot, cook potatoes, carrots and celery in water until tender, about 20 minutes. Drain, reserving liquid and setting vegetables aside. In the same pot, saute onion in butter until soft. Stir in flour, salt and pepper; gradually add milk, stirring constantly until thickened. Gently stir in cooked vegetables. Add reserved cooking liquid until soup is desired consistency. Yield: 8 servings.