For the Sacher cake, cream the butter with the powdered sugar and vanilla sugar until fluffy. Fold in melted chocolate. Stir in yolks one at a time.
Beat egg whites with granulated sugar until stiff and stir into the fat mixture. Fold in flour and baking powder. Bake at 190 degrees needle test.
After cooling, cut the cake once, fill with jam and reassemble. Spread the outside of the cake with jam and cover with chocolate icing.