Fill a large stock pan with water, add whole potatoes and bring to boil- allow potatoes to boil for approx. 15 minutes (until they are tender enough to easily pierce with a fork).
Strain potatoes under cold water, peel the skins while they are under the water (they should fall off easily).
Once skins are removed, coarsely chop the potatoes and add them to a large bowl. Refrigerate one hour, until they are no longer warm.
Add very finely chopped (finely chopped is KEY) celery and onion and mix.
Dissolve sugar in warm water and pour over potato mixture. Add mayonnaise, mustard, vinegar, salt & pepper- mix well.
Garnish with finely chopped celery leaves (optional) and enjoy!
You may need to add a bit more mayo, salt and pepper depending on your personal preference. If the potato salad is refrigerated overnight it can tend to dry out a bit, so I usually add a bit more mayo before serving.