First boil the berry mix with the raw cane sugar, puree and boil again with potato starch – let cool.
In the meantime, separate the eggs. Mix egg yolks with powdered sugar, vanilla sugar and lemon zest until foamy. Beat egg whites with a pinch of salt until stiff. Alternately mix the beaten egg whites and flour into the yolk mixture.
Spread on a baking tray lined with baking paper and bake at 180 °C for 10-15 minutes. In the meantime, mix the curd with the berry mix.
Place the sponge on a tea towel, peel off the baking paper and spread with the curd-berry mixture. Roll up and enjoy.