For the sponge cake, beat the eggs, powdered sugar and vanilla sugar until foamy. Sift flour with baking powder and fold into the yolk mixture. Line a baking tray with baking paper, spread the sponge and bake at 190 °C for approx. 15 minutes.
Turn out the sponge cake and remove the baking paper. Mix the apricot jam and rum and immediately fill the sponge cake and roll it up. Sprinkle with powdered sugar if desired.