Beat the butter until foamy, add sugar, vanilla sugar and a small pinch of salt and continue to stir. Add the eggs and stir. Mix the flour with the baking powder and stir into the batter. Finally add the milk. If you used large eggs, omit the milk.
Wash, halve and stone the plums.
Put the dough in the greased 18 cm springform pan. Spread the half plums on top with the cut side up. Put almond sticks on top if desired. Sprinkle with cinnamon sugar.