Wash potatoes thoroughly and cook in boiling water for about 20 minutes. Peel and finely dice the onions. Bring the stock, vinegar, onions, salt, pepper and sugar to the boil and simmer over a low to medium heat for 8-10 minutes. Then drain the potatoes, rinse and peel. Cut potatoes into slices, place in a large bowl and pour stock over them. Leave to stand for about 1 hour, stirring carefully 2-3 times.
In the meantime, clean and wash the radishes and, except for one radish for garnishing, quarter them. Wash and peel the cucumber, quarter it lengthwise and cut it into pieces. Wash chives, shake dry and cut into small rolls
Cucumber, radishes and chives, up to 1 tablespoon for sprinkling, carefully fold into the potatoes. Mix remoulade and soured milk, mix carefully under the potatoes. Leave to stand for approx. 45 minutes. Arrange the salad in a bowl sprinkled with chives and garnish with radishes
waiting time approx. 1 1/2 hours