Preheat oven to 325 degrees and grease the base of 10 inch round form.
Beat egg whites very stiff. Stir in the softened butter or margarine with a hand mixer until it becomes smooth. Gradually add sugar and vanilla sugar, stir until mixture has thickened. Add egg yolks one at a time, whisking with mixer at the highest setting.
Mix together cocoa powder and baking powder, sift, add the hazelnuts and grated chocolate to the egg mixture in 2 stages and stir briefly using the medium setting on your mixer.
Put the cake mixture in the springform and smooth the surface.
Place in oven for about 30 minutes.
Leave cake in tin for about 10 minutes after taking out of the oven.
After removing from form place on cooling rack.
When cool, scoop out cake with a spoon to a depth of 3/8 inch, leaving a rim of about 3/8 -3/4 inch. To ensure a neat rim, cut round the cake with tip of a knife before scooping out the middle.
Crumble the scooped out cake in a bowl.
For the filling drain the cherries and place on a paper towel.
Peel the bananas, cut in half lengthways, sprinkle with lemon juice and arrange in scooped out cake.
Arrange the cherries on top.
Whip the cream with sugar and vanilla sugar, spoon on the fruit to form a dome.