Separate eggs. Beat the egg white with the whisk of the hand mixer until stiff, adding 75 g sugar and salt. Stir in egg yolks. Mix flour and baking powder, sieve over the egg cream, fold in carefully. Line a baking tray (32 x 39 cm) with baking paper. Pour the mixture on top and spread evenly.
Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for about 12 minutes. Turn out onto a tea towel sprinkled with sugar. Carefully remove the baking paper. Roll up with the cloth from the short side, allow to cool. In the meantime cut melons in half and cut out approx. 300 g balls with a small ball cutter. Cut out 10 balls with an even smaller ball cutter and chill them for decoration. Use the rest for other purposes. Soak gelatine in cold water. Mix buttermilk, yoghurt, 100 g sugar and vanillin sugar. Squeeze the gelatine, dissolve carefully. Mix with some buttermilk yoghurt, then stir everything into the remaining buttermilk yoghurt mixture. Whip 150 g cream until stiff.
Use the rest for other purposes. Soak gelatine in cold water. Mix buttermilk, yoghurt, 100 g sugar and vanillin sugar. Squeeze the gelatine, dissolve carefully. Mix with some buttermilk yoghurt, then stir everything into the remaining buttermilk yoghurt mixture. Whip 150 g cream until stiff. As soon as the buttermilk yoghurt mixture begins to gel, carefully fold in the cream. Pour the cream onto the sponge cake plate, smooth it down and sprinkle with melon balls, then roll it up. Chill for about 3 hours. Shortly before serving, whip 100 g cream until stiff. Put the cream in a disposable piping bag and squirt small tuffs onto the sponge roll. Decorate with remaining melon balls and mint leaves
As soon as the buttermilk yoghurt mixture begins to gel, carefully fold in the cream. Pour the cream onto the sponge cake plate, smooth it down and sprinkle with melon balls, then roll it up. Chill for about 3 hours. Shortly before serving, whip 100 g cream until stiff. Put the cream in a disposable piping bag and squirt small tuffs onto the sponge roll. Decorate with remaining melon balls and mint leaves
3 1/2 hours waiting time