Preheat the oven to 200°C.
For the cake: Separate the egg whites and yolks. Whisk the egg whites with salt until stiff. Whisk the egg yolks with the sugar and vanilla sugar until thick and creamy. Add the egg whites to the yolk cream, sift the flour and starch and carefully fold the flour in the egg cream. Evenly spread out the batter on a parchment-lined baking sheet. Bake in the oven for about 12 minutes. Turn out onto a sprinkled with sugar tea towel, remove the baking paper and roll in the cake with the towel starting from the longer side. Cool down for about 1 hour.
For the cream: Mix the cream cheese with the quark cheese and vanilla sugar until smooth. Beat the cream cheese mixture with the whipped cream until stiff. Set aside and refrigerate about 1/4 of the cream for decorating.
Roll the cake apart again and brush with cream. Peel the banana and brush with lemon juice. Lay out the banana on the lower third of the filling. Roll in the cake. Using the leftover cream, cover the cake roll. Fill the cream set aside for decorating into a piping bag with a serrated nozzle and decorate the roll. Chill the cake for at least one hour.
Decorate the sides of the roll with nut brittle. If you wish, you can also decorate the roll with M&Ms.