Peel the orange so that the white skin is completely removed. Cut the flesh from the parting skins. Collect the juice. Drain mandarin oranges on a sieve.
Mix quark, milk, 3 tablespoons of orange juice, rum, sugar and vanillin sugar. Roughly chop the chocolate and stir into the quark mixture, except for a little bit for sprinkling. Add mandarins and orange filets, except for a few for decoration, to the quark mixture and fold in carefully.
Fill into small bowls, sprinkle with remaining chocolate and cover with remaining orange and tangerine slices. Serve decorated with lemon balm if desired.