Just diced potatoes, celery, onions, and water...boil until soft. I would mash some of the potatoes for thickening, then add whole milk and some heavy cream (if there is a lot of potato water) salt and pepper and serve. DIL would serve with sides of bacon bits, shredded cheese and crackers.
My little GD was staying with me one day when I made potato soup and I told her DH would eat it with about a million buttered crackers, she cracked up! He loved this soup... No SOUR CREAM.