Wash, halve and stone the damsons.
Marinate the plums in sugar and cinnamon.
Preheat oven at 190°C hot air. Grease the cake tin, 24 cm diameter, with enough butter. I always like to use a kitchen paper instead of a kitchen brush.
Beat the whipped eggs, sugar, lemon grater and vanilla sugar until foamy for 4 minutes.
Add baking powder, flour and butter to the mixture and mix for another 3 minutes.
Add some brown rum to the dough.
The dough must fall from the spoon tear-resistant. If the rum makes the dough too soft, add some flour.
Pour the cake mixture into the baking tin and spread evenly with the cake spatula.
Place the plum halves marinated with sugar and cinnamon, inside down, in the dough.
Bake the plum cake for 30-35 minutes at 180°C, remove the ring from the baking tin while still hot and allow the fruit cake to cool.
Sprinkle the cake with icing sugar for decoration. Use a fine sieve.