For the potato dressing cook the potatoes for about 25 minutes. Drain, rinse and peel. Press immediately through a potato press, let cool.
Onions peel, finely dice. Mix with potatoes, 200 ml vinegar and mustard. Fold in 8 tbsp. oil. Season with salt, pepper and sugar.
Halve chicory and radicchio lengthwise, remove stalk. Wash lettuce leaves and lamb's lettuce, spin dry. Pluck larger lettuce leaves finely. For the vinaigrette, mix 4 tablespoons of vinegar with some salt, pepper and 1⁄2 tsp. sugar.
Emulsify 2 tablespoons of oil. To serve, first mix the salad with the vinaigrette, then drizzle potato dressing over it. Pluck the cheese into pieces and place on top.