Peel potatoes and cut into about 1 inch cubes. Cover potatoes with cold water in a large pot and bring to a boil. Simmer until fork tender.
Drain water and pour 1/2 to 3/4 cup apple cider vinegar over hot potatoes, cover and let stand.
Meanwhile boil eggs (hard boiled), peel and let cool. When eggs are cool enough to handle cut in half, remove the yolk to a small bowl, grate the whites.
Sprinkle potatoes with dried parsley and add the grated whites and diced onions to the potatoes.
LIBERALLY sprinkle with celery salt (this will be the only seasoning. I use at least two tablespoon depending on how many potatoes I am using)
Mash the egg yolk, add plenty of mustard (start with a couple tablespoons), mayonnaise (a seriously unhealthy amount; start with ~ 1 cup) and mix well. Add this mixture to the potatoes and mix throughly.
Let flavours develop and add more celery salt and/or mustard if needed.