Mix the icing sugar with the egg yolks until frothy. Gradually stir in the oil, flour, starch, baking powder and the custard powder. Add the egg liqueur to this mixture and mix everything well. Beat the egg whites until stiff and finally fold them into the dough.
Pour the mixture into a bundt pan and bake at 160 degrees for about 1 hour.
This cake is made so fine by the addition of powdered sugar instead of normal sugar.