Wash the potatoes and cook them with the water in a pot as jacket potatoes for about 35 - 40 minutes, let them cool down a little and peel them while they are still lukewarm. Peel the onions and dice them with the multi chopper or a knife. Wash the cucumber and grate finely with the peel (if unsprayed, otherwise peeled) and place in a bowl with the chopped onion. Cut the potatoes into slices and add. Season well with vinegar, salt, pepper, mustard, sweetener or sugar and the hot vegetable stock to taste, add oil and mix well. If you want, you can sprinkle chives on top. The salad should sit through for an hour!