Grease a deep 9 inch spring from pan and line with parchment or wax paper.
Place 8 oz bittersweet chocolate 1/2 cup butter and milk into a saucepan. stir over low heat until smooth. Remove from heat, beat in sugar and vanilla and cool slightly.
Beat egg yolks and sour cream in a bowl, then beat into chocolate mixture. sift the flour and baking powder over surface and fold inches.
Whisk the egg whites in a grease free bowl (not plastic) until stiff. fold into mixture.
Pour into prepared pan and bake for appx 45-55 minutes-until a toothpick comes out clean. Cool in the pan for 15 minutes then invert onto a wire rack to cool.
Slice the cooled cake across the middle to make three even layers.
Make the filling: In a small saucepan, warm the jam with 1 tbls of brandy or cognac an brush over the layers; let sit. Place the remaining brandy ( I usually add more) in a pan with 14 oz of bittersweet chocolate and 7/8 cup of butter. Heat gently, stirring until smooth. Cool the mixture until it starts to thicken.
Spread the bottom layer of the cake with half the chocolate filling taking care not to disturb the jam.Top with second layer and spread with remaining chocolate filling. Top with final layer and press down lightly.
Make Ganache: Heat the cream and the semi sweet chocolate together over low heat stirring frequently until chocolate has melted. Pour into bowl, let cool, then whisk until mixture begins to stiffen.
After cake has set, spread the top and sides of the cake with ganache and decorate with chocolate curls or chocolate leaves.