Wash potatoes thoroughly and cook in boiling water for about 20 minutes. In the meantime mix vinegar and stock. Fold in the oil. Wash chives, dab dry and cut into small rolls. Wash the cucumber, rub dry, cut in half crosswise and cut into fine strips around the core using a peeler. Clean and wash the radishes and cut them into slices.
Cold quench the potatoes, peel them and, depending on their size, possibly halve them. Mix potatoes and stock. Add the remaining ingredients and carefully fold everything in. Season to taste with salt and pepper. Wash the radish sprouts, dab dry and place on top