Wash the untreated orange, cut off 4 thin slices and set aside. Squeeze the rest of the orange. Peel 2 oranges including the white skin. Cut them into slices, sprinkle with liqueur if necessary. Cut the rest of the orange in half, squeeze the juice
Stir the soured milk and quark until creamy. Stir in all the orange juice and vanilla sugar. Season to taste with sugar
Arrange peeled orange slices in 4 dessert glasses. Fill with curd cheese. Chop the cherries. Decorate quark with the untreated orange slices, pistachios and cherries