Beat the eggs and hot water with the hand mixer and whisk on the highest setting for 1 minute until frothy. Mix the sugar and vanilla sugar, slowly sprinkle in and beat the whole thing for about 2 minutes. Mix the flour, cornstarch and baking powder and slowly sift in addition. Mix in everything on the lowest setting with the whisk.
Bake the sponge cake at 175 ° C for about 20 minutes. The temperature and baking time depend on the oven.
Let the sponge cake cool and cut it lengthways once.
Drizzle with the espresso and the liqueur.
Whip the cream with the cream stabilizer, sugar and vanilla sugar until stiff. Stir the mascarpone until smooth and fold in the whipped cream. Spread half of the cream on the sponge cake, then place the second sponge cake on top and spread the other half of the cream on top.
Just before serving, dust the cocoa powder over it.
I bake the biscuit in an Ikea baking dish (20 cm wide and 30 cm long).
If you want to save yourself the bake, you can of course also use ladyfingers. I find these too sweet myself, so I bake a sponge cake that is not so sweet and fluffy.