For the dough, separate the eggs, bring butter to room temperature.
In a bowl, cream butter with powdered sugar and stir in yolks and vanilla sugar.
Melt the chocolate in a bain-marie, but do not let it get too hot, and add to the mixture.
Beat the egg whites with the granulated sugar until stiff and carefully fold into the rest of the mixture. Finally, gently stir in the flour.
Butter a cake springform pan well and dust with flour, pour in cake batter and bake in oven preheated to 180 °C for about 1 hour.
Allow the cake to cool, then cut in half. Spread both cake layers with a very thin layer of strained, slightly warmed jam and put them back together.
Then brush the outside of the Sachertorte with jam as well before frosting with chocolate icing.
Brushing the outside of the Sacher cake with jam makes the icing especially nice and smooth.