Wash the potatoes and cook in boiling water for about 20 minutes. In the meantime peel the onions. Dice 1 onion finely and cut the other one into fine rings. Mix quark, 250 g sour cream and linseed oil.
Season to taste with salt, pepper and sugar. Wash the chives, dab dry and cut into fine rings, except for a little bit for garnishing. Fold onion, except for a few rings for garnishing, and chives into the quark.
Mix 250 g sour cream and lemon juice. Season to taste with salt and sugar. Wash the salad, dab dry and pluck into bite-sized pieces. Mix salad and sour cream dressing. Drain potatoes, rinse with cold water and peel.
Arrange everything together and garnish with remaining onion rings, chives and lemon slices.