Preheat oven to 180°C (350°F).

Beat egg yolks with sugar and vanilla sugar until pale yellow. Add flour and baking powder. Mix until you get an homogeneous paste.

Whisk egg whites until foamy. Incorporate delicately in the previous mixture.

Spread in a thin layer on a baking tray previously covered with greaseproof paper.

Bake until coloured a light gold, about 10 to 15 minutes. Monitor baking process after 10 minutes. It took me exactly 12 minutes.

Remove cake from baking paper and replace on top of it.

Cover cake with jam and roll cake using baking paper.

Refrigerate for 1 hour.

Remodel your cake if needed.

Cut both ends using a bread knife and decorate with some powdered sugar.