Mashed Potato Soup

1 Tablespoon Chopped Onion
1 Tablespoon Butter or Margarine
2 C. Milk
1 1/2 C. Prepared Mashed Potatoes
1/2 teaspoon Salt
1/9 teaspoon Celery Salt
1/8 teaspoon Pepper
1 Tablespoon Minced fresh or dried chives

In a saucepan, saute the onion in butter until tender. Add milk, potatoes, salt & celery salt if desired and add pepper; heat through. Garnish with chives (and sour cream)