Preheat oven to 350°F. Line a baking sheet with parchment paper.
In a large bowl, cream together butter, sugar, and vanilla sugar until light and fluffy. Beat in the eggs one at a time.
Mix flour with baking powder, cocoa, and salt. Alternately add the dry ingredients to the milk mixture, stirring gently after each addition until just combined. Pour the batter onto the sheet and bake for about 30 minutes. Afterwards, let it cool.
For the filling, finely chop the dark chocolate. Whip the heavy cream with gelatin/pudding mix and extract until stiff. Fold in the chopped chocolate.
Using a tablespoon, hollow out the cake base, leaving a 2 cm border around the edges. Crumble the removed cake and set the crumbs aside.
Peel the bananas and halve lengthwise. Spread them on the base.
Spread the whipped cream over the bananas and edge of the cake.
Sprinke the cake crumbs and gently press them into the cream. Refrigerate the cake for 2 hours before serving.
