Fillet the oranges and grapefruits. Peel the rudolines and remove the white skin from the wedges:. Marinate the citrus fruits with orange liqueur, brown sugar and the pistachios.
For the gratin mixture, mix egg yolks with powdered sugar until creamy. Stir in cornflour, strained quark and rum, lemon zest and vanilla sugar. Whip egg whites with granulated sugar until stiff, fold into curd mixture.
Grease heat-resistant soup plates precisely with butter. Evenly distribute marinated citrus fruits on the plates and cover with curd mixture. Preheat the oven to maximum temperature. Bake curd mixture in oven at maximum top heat for 8 to 10 minutes until au gratin.
Serve citrus fruits au gratin sprinkled with powdered sugar and garnished with mint leaves.
Kaisergarten, sweet wine rich in extract