Preheat oven to 150°C. Mix eggs, flour, sugar, mineral water and oil to a dough. Then spread the dough evenly on a greased baking sheet and bake in the preheated oven for 20 min. Then let the cake cool down a bit. Spread the plum puree on the bottom.
Then whip the cream, vanilla sugar and cream stiffener until stiff. Carefully fold the sour cream into the stiff cream and spread on the plum puree. Finally, add the sugar and cinnamon on top of the cream.