Wash the potatoes and cook for about 40 minutes. In the meantime, wash and drain the sprouts. Wash the cucumber, first cut into slices, then into strips. Wash, clean, quarter and seed the tomato.
Cut the fruit flesh into small cubes. Mix sprouts, cucumber, tomato and crab flesh. For the marinade, beat lemon juice and oil. Season with salt, pepper and sugar. Mix with the salad, season again.
Cut the potatoes crosswise and break open a little. Spread the salad on top. Mix yoghurt and crème fraîche. Spread the salad on top as well. Serve garnished with lettuce leaf, lemon slice and dill.