Wash the potatoes and cook in boiling salted water for 15-20 minutes. In the meantime cut the sausage into slices. Drain the mandarins and collect the juice. Peel and finely chop 1 onion.
Clean, wash and cut the celery into small pieces. Blanch in boiling salted water for about 2 minutes and drain. Peel and slice the potatoes. Sauté diced onions in hot oil.
Deglaze with vinegar and tangerine juice, bring to the boil. Season with salt and pepper. Mix marinade with potatoes, sausage, mandarins and celery. Cover and leave to stand for about 30 minutes. Mix mayonnaise and mustard.
Season with brandy and add to the salad. Peel the rest of the onion, cut into rings and turn in paprika. Garnish salad with it and serve sprinkled with chervil.