A sweet, red wine Auslese is more subtle than a port wine, but has enough body to stand up to a moist, autumnal cake and is the perfect addition to any coffee gathering.
Preheat the oven to 180°C/350°F. Halve plums and remove pits.
Add part of the butter and part of the sugar to a stand mixer and beat until light and fluffy. Add eggs and beat until well incorporated. Add part of the flour and baking powder. Beat until a smooth dough has formed.
Transfer dough onto a lined baking sheet, spreading it out evenly to create a smooth surface.
In a large bowl, mix remaining butter, sugar, flour, and vanilla sugar into coarse crumbles with your fingers.
Arrange plum halves on the dough in overlapping rows, cut side facing up. Sprinkle a thick layer of crumbles on top of the cake and bake in preheated oven at 180°C/350°F for approx. 1 h. Dust with confectioner’s sugar before serving and enjoy with whipped cream or vanilla ice cream, if desired.