Cook the potatoes in their skins in salted water until cooked.
In the meantime, clean and wash the radishes, cut them into slices and cut the slices into strips, sprinkle with a little salt and let them steep.
Cut the bacon into fine cubes, roast in the pan and drain the bacon cubes on paper towels. Cut the chives into rolls.
In a large bowl with mineral water, stir the yoghurt until smooth, add the radishes, bacon and chives and season with pepper, lemon juice and possibly a little salt.
Peel the potatoes, sprinkle with cress and serve with the radish yoghurt.
The radish yoghurt can also be served as a dip with crackers or vegetable sticks, then cut the radishes into very fine strips.