Swiss Potato Soup
["1 large onion, chopped", "3 Tbsp. butter", "3 large potatoes, pared and cut up", "2 tsp. salt", "1 tsp. dry mustard", "1/8 tsp. white pepper", "3 c. water", "2 c. milk", "1 (8 oz.) pkg. sliced Swiss cheese, cut up", "2 Tbsp. chopped celery", "parsley (optional)"]
["Saute onion in butter until soft in a large kettle.", "Stir in potatoes, salt, mustard, pepper and water.", "Heat to boiling. Cover and simmer 30 minutes or until potatoes are soft.", "Pour soup, a little at a time, into blender or food processor.", "Process until smooth.", "Return to kettle.", "Stir in milk; heat slowly until it boils.", "Stir in cheese.", "Pour in bowls; sprinkle with parsley."]
["onion", "butter", "potatoes", "salt", "dry mustard", "white pepper", "water", "milk", "Swiss cheese", "celery", "parsley"]