Comforting Potato Soup - cooking recipe

Ingredients

3 medium potatoes, peeled and sliced
1 carrot, diced
3 stalks celery, diced
1 quart water
1/2 onion, chopped
1 1/2 tablespoons butter or 1 1/2 tablespoons margarine
3 tablespoons flour
1/2 teaspoon salt
1/4 teaspoon pepper
1 1/2 tablespoons parmesan cheese
1/4 teaspoon dry mustard
3/4 cup 2% low-fat milk

Preparation

In large pot, cook potatoes, carrots and celery in water until tender, about 20 minutes.
Drain, reserving liquid and setting vegetables aside.
In same pot, saute onions in butter until soft.
Stir in flour, salt, pepper, parmesan cheese and dry mustard.
Gradually add milk, stirring constantly until thickened.
Gently stir in cooked vegetables.
Add 1/2 cup or more of reserved cooking liquids until soup is desired consistency.