Cook potatoes, celery, and onion in a saucepan with about 1 – 11⁄2 inches of water for about 15 – 20 minutes.
Remove from water, add butter and milk. Let simmer.
Mash potato mixture and add to liquid. Let simmer.
Add salt and pepper to taste.
May add green peppers, bacon, broccoli, and/or Velveeta cheese after soup is nearly done.