For the plum tart, first prepare the sponge.
To do this, mix the baking powder and flour, add the remaining ingredients and mix with the whisk of the mixer on high speed for about 1 minute until smooth. Pour the dough into a 26 cm diameter cake springform pan lined with baking paper.
Bake for about 30 minutes in a preheated oven at 170 degrees. Immediately remove the base from the pan, turn out onto a cake rack lined with baking paper, let cool, divide once.
For the plum cream, soak gelatine according to instructions. Remove the seeds from the plums and puree them. Add sugar, vanillin sugar and cinnamon and refine with the Slivovitz.
Gently squeeze the soaked gelatin, dissolve, stir into the plum mixture and refrigerate. When it starts to gelatinize, fold in the whipped cream.
Spread the bottom layer with the plum cream, cover with the top layer. Place a tortering around it.refrigerate the cake for 3 hours.
For decorating, whip the whipped cream with the cream stiffener and vanillin sugar until stiff.
Spread some of it on the edge of the cake and decorate with a cake garnishing comb. Decorate the edge of the cake with the remaining whipped cream (piping bag with star nozzle).
Finally, garnish the plum cake with chocolate shavings and halved plums.