Cut the roast pork into strips about 3 cm long. Wash apples, quarter, core and cut into thin slices. Squeeze 1 lemon and drizzle the juice immediately over the apple slices to prevent them from turning brown.
Clean, wash and pluck the frisée salad. Mix the meat, apples, lettuce and hazelnuts and place in a bowl. Squeeze the second lemon. Mix sour cream with mayonnaise and season to taste with lemon juice, salt, pepper and sugar.
Serve the sauce separately with the meat salad.