In a food process or blender place the chopped dark chocolate, pulse to grind. Set aside.
Preheat oven to 350ºF. Grease and lightly flour two 9” round cake pans.
In a medium bowl combine flour, 3 tablespoons of the ground dark chocolate, baking soda, and baking powder.
In a large bowl beat the eggs and sugar until foamy and pale in color. Add the vanilla and ¼ cup of the brandy liqueur. Alternately fold in 1/3 of the flour and ½ of the milk, ending with the flour. Fold in the mayonnaise. Divide the batter evenly between the two prepared pans. Bake for 30-35 minutes or until centers spring back upon touch. Cool for 10 minutes in pans. Remove from pans and cool on wire racks for 1 hour before Frosting.
In a saucepan melt the fruit preserves. Add the blackberries and ¼ cup of the brandy liqueur and cook for 5 minutes until thickened. Set the filling aside to cool.
Ina large bowl beat the butter until fluffy. Add the confectioners sugar and slowly add the remaining ground dark chocolate and the coffee until creamy.
Split the cake layers in half. Spread the bottom layer with half of the fruit filling. Place the next layer on and top with ¼ of the frosting. Add the third layer and top with remaining fruit filling. Add the last layer and Frost the sides and top with remaining frosting.
Decorate if desired with shaved chocolate and fresh blackberries if desired.