Wash the potatoes thoroughly. Cook in boiling water for about 20 minutes. Remove and wrap in aluminium foil. Cook in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for another 20-30 minutes.
Wash the herbs, dab dry, put some dill aside for garnishing. Finely chop the rest. Cut sorrel into fine strips. Cut chives into small rolls. Set aside some sorrel and chives.
Mix crème fraîche, yoghurt and mustard. Stir in herbs. Season to taste with salt and pepper. Clean and wash the salad and drain well. Wrap the potatoes in foil, cut lengthwise and press them apart a little.
Fill with about 3/4 of the herb sauce. Serve with salad. Dribble the rest of the sauce onto the salad. Sprinkle with herbs that have been set aside.