Preheat the oven to 180°C and grease a 23cm round cake tin.
Melt the chocolate gently in a bowl over hot water and cool slightly.
Beat the butter and sugar together until light and fluffy.
Stir in the melted chocolate, vanilla extract, and egg yolks.
Fold in the ground almonds and sieved flour.
Whisk egg whites to stiff peaks and fold gently into the batter.
Bake for 45-50 minutes until the cake springs back when pressed.
Cool on a wire rack then brush the top and sides with warm apricot jam.
Melt plain chocolate into hot cream to create a smooth icing.
Pour icing over the cake and pipe 'Sacher' using melted milk chocolate.