Shortcrust pastry: Knead the ingredients for the shortcrust pastry first with a hand mixer (dough hook) and then by hand to a smooth dough. Form this dough into a ball, wrap in cling film and place in the refrigerator for about 30 minutes. Preheat the oven to 170 degrees top and bottom heat. Grease the bottom of a cake springform pan (28 cm) diameter, roll out the dough on a floured surface and place it on the springform pan bottom. Trim off the overhanging edges. Bake the short pastry for about 15 minutes until golden brown, remove from the base and cool on a wire rack.
Sponge cake bases: For the sponge cake bases, preheat the oven to 170 °C top and bottom heat. For the light sponge cake, first beat the eggs with the water, sugar and vanilla sugar until a thick whitish cream is formed and the sugar has completely dissolved. Mix flour with baking powder and cornstarch and fold into the egg cream. Pour the dough into a cake springform pan (28 cm ø) lined with parchment paper and bake for about 25 to 30 minutes. Then make a second sponge cake as described, but mix the flour, cornstarch and baking powder with the cocoa. Pour the dough also into a cake springform pan and bake. Remove the bases from the mold and cool on a wire rack. When the cookies are completely cool, cut both bases once horizontally.
Cake: Whip the cream with the cream stiffener and vanilla sugar until stiff.