Wash the oranges in hot water, dab dry. Cut off a large lid from each of 4 oranges at the base of the stalk. Hollow out the oranges. Peel the peel of the fifth orange in strips, rub off the remaining peel. Peel the orange so that the white skin is completely removed.
Cut out all the fillets between the parting skins and collect the juice. Squeeze the remains. Cut all but a few fillets into small pieces.
Mix quark, 4 tablespoons orange juice, grated zest, liqueur and vanillin sugar. Season to taste with sugar. Chop brown cake coarsely and, except for some for decoration, stir in with the orange pieces
Fill the hollowed oranges with curd cheese. Arrange with remaining orange fillets and sprinkle with remaining brown cake. Decorate with strips of orange peel and mint
Hollow out oranges: cut along the inside of the peel, cut the flesh lengthwise and remove from the centre with a tablespoon