Beat the butter, vanilla sugar and sugar until fluffy. Add the flour, chestnut flour, vanilla pudding powder, baking powder, lemon zest, salt, mineral water and cream and work into a smooth dough. Place the dough in the springform cake tin. Peel the apple and cut it into 1 cm thick slices. Mix the apple with the cinnamon, sugar and lemon juice. Spread the apple slices over the cake in a fan-like pattern. Bake for approx. 45 min. at 180 °C in a fan oven.