Mix vinegar and mustard, fold in 2 tablespoons of oil. Season to taste with salt, pepper and sugar. Bake the Rösti in a preheated oven (electric cooker: 225 °C / circulating air: 200 °C/ gas: level 4) for approx. 20 minutes, turning once.
Clean, wash and cut the spring onions into 12 pieces. Cut the cheese into twelve 10 cm long sticks. Spread the ham slices with horseradish and season with pepper. Spread the spring onions and cheese on top and roll up.
Pin it with wooden skewers. Heat 2 tablespoons of oil in a pan. Fry the ham rolls in it at medium heat for about 10 minutes all around. Clean and wash the lamb's lettuce. Wash, quarter, core and slice the apple.
Drain the beetroot and dice roughly. Peel and finely dice the onion. Mix the salad ingredients with the vinaigrette. Arrange rösti corners, ham rolls and salad on plates.