Beat egg yolks and sugar until foamy. Mix 3 tablespoons of water with oil and mix flour with cornstarch and baking powder. Stir both into the egg yolk mixture and finally add cocoa. Beat egg whites until stiff and then fold into the batter.
Place the dough on a baking tray lined with baking paper and bake in a preheated oven at 180 °C for approx. 20-25 minutes.
Once the dough is baked, remove from the oven and cut in half. Remove one half from the tray and leave the other half on the tray. Prick the half on the tray with a fork and drizzle with black coffee. Let the coffee really soak into the dough.
Prepare the cream. Mix 2 tablespoons of flour in 200 ml of milk. Stir well, because there should be no lumps inside. Add the egg yolks, powdered sugar and vanilla sugar. Cook the mixture over a low heat until it thickens. Remove the thick mixture from the heat and let it cool down a bit. Now stir in butter and melt it in the warm mass while stirring constantly.
Now prepare the white layer. Heat water with sugar. When the sugar has dissolved, remove from heat and let cool slightly. Beat egg whites until stiff and add warm syrup in batches, continuing to beat. The beaten egg whites must be firm.
Spread the butter cream on the pastry soaked with coffee, place the other pastry sheet on top, spread the beaten egg whites and cover with a chocolate glaze made of melted chocolate mixed with oil. Then refrigerate. Enjoy it!
