For the potato salad, wash the potatoes and boil them in a pot until they are soft, but not yet disintegrated. Meanwhile, cut the onion and prepare the marinade.
Mix vinegar, water, salt and a pinch of pepper. Cool the hot cooked potatoes, peel and slice them.
Mix in the onion and empty the marinade over the potatoes while they are still lukewarm, so that the salad can still steep.
Before serving, pour the sunflower oil over the salad and mix well again.