Wash the potatoes and cook in boiling water for about 20 minutes. Rinse, peel and let cool off. In the meantime, peel and finely dice the onions. Bring the stock to the boil, add mustard, vinegar and diced onions and let it cool down a little.
Wash the dill, put something aside for garnishing. Chop the remaining dill finely. Cut potatoes into slices. Add stock, dill and oil, mix carefully and let it soak through a little. Season to taste with salt and pepper before serving.
Pour potato salad into a bowl. Garnish with dill and dill flowers.