Grease the bottom of a springform pan (18 cm) and sprinkle with breadcrumbs. Preheat the oven to top / bottom heat approx. 180 ° C, hot air approx. 160 ° C.
Mix egg yolks, sugar and vanilla sugar until frothy. Stir in water and oil. Mix flour with baking powder and gradually stir in. Beat the egg whites until stiff and fold into the batter. Halve the dough and stir the cocoa into one half of the dough.
First, put 2 tablespoon of the light-colored batter in the center of the springform pan (do not spread!). Put 2 tablespoons of the dark dough on the light dough (not next to it). Repeat the process until the batter is used up. Do not smooth the dough. Put in the oven and bake for about 40 minutes.
Remove the cake from the mold and let it cool on a wire rack.
Mix the powdered sugar with the orange juice and cover the cooled cake with it.