For the oil cake, separate the eggs and beat the yolks with the sugar and vanilla sugar until foamy. Slowly add oil and water and continue to beat.
Mix flour with baking powder and cocoa and sift over the yolk mixture. Beat egg whites with a pinch of salt until stiff and fold in. Grease and flour a cake pan and pour in the batter.
Bake in the preheated oven at about 180 °C for about 40 minutes.