For the Danube waves with bananas, cream butter, powdered sugar, vanilla sugar and salt. Separate the eggs and stir in the egg yolks. Beat the egg whites with the granulated sugar until stiff, sift the baking powder into the flour and add to the mixture. Finally, carefully add the beaten egg whites.
Now spread half of the mixture on the baking tray. Mix the second half of the mixture with the cocoa and spread it over the light mixture. Place the bananas on the dough and press down a little. Bake in the oven at 180 degrees for 25 minutes.
For the cream, prepare the vanilla pudding and let it cool down well. Mix butter, powdered sugar and egg liqueur until smooth and spoon in cold pudding and stir until fluffy.
To finish, spread the custard over the cooled cake. Then apply the chocolate frosting. For the famous waves, apply the chocolate in small round circles one after the other. Then use a knife to connect the circles in a wave shape. Then leave to cool.