In the meantime, heat some butter in a saucepan and sauté the onion, cut into fine cubes, until translucent. Then deglaze with water and add the stock cube. Season the broth with salt, pepper, nutmeg, mustard, maggi and fondor. It is important that the broth is very strong as the potatoes will soak up a lot. So it can be salty and spicy.
Peel the cooked potatoes and let them cool down briefly until you can touch them. Slice the potatoes into a bowl with a slicer and immediately pour the hot broth over them. Mix briefly and let steep for about 10 minutes. Add the vinegar, stir and add the oil to the salad just before serving.
The potato salad goes perfectly with peeled dumplings.