Grease the cake tin and preheat the oven to 160°C.
Separate the eggs, whisk the egg whites with a pinch of salt and chill the whites. Cream soft butter with yolks, add vanilla sugar and powdered sugar, add 2 tablespoons rum. Stir the curd until creamy and mix into the mixture by the spoonful. Add the grated zest of a lemon and orange, squeeze half a lemon and orange and stir into the dough.
Mix flour with baking powder and cornstarch and fold into the batter. Add a little milk as needed. Finally, fold in the beaten egg white.
Pour the batter into the cake pan and bake at 160 °C for about 60 minutes.
Allow the curd cheese cake to cool, turn out and sprinkle with powdered sugar.