For the dough, place the eggs and egg yolks in a mixing bowl and stir with a hand mixer and whisk on the highest setting for 1 minute until foamy. Mix the sugar and vanilla sugar, sprinkle in for 1 minute and beat for another 2 minutes. Mix the flour with the cornstarch and baking powder, sift half of it onto the custard and stir in briefly on a medium heat. Work in the rest of the flour mixture in the same way.
Spread a good two thirds of the dough on a baking sheet lined with baking paper (30x40cm, greased, lined with baking paper), crease the paper in the open area of the sheet immediately in front of the dough, so that an edge is created. Briefly stir in the sifted cocoa powder and water into the remaining dough, place in a freezer bag, cut off a corner that is not too small and sprinkle zebra stripes on the light dough. Put the baking sheet in the oven.
Top / bottom heat: approx. 220 c (preheated)
Hot air: approx. 200 c (preheated)
Gas: level 4-5 (preheated)
Baking time approx. 10 min
Immediately after baking, turn the sponge cake out onto a sugar-sprinkled tea towel and let it cool with baking paper.
For the filling: wash the berries, drain them, clean them and cut the strawberries into pieces. (Leave 6 strawberries or approx. 12 blueberries, 12 raspberries etc. to decorate). Remove the baking paper from the biscuit plate and spread the yoghurt on top. Whip the cream with sugar and cream stiffener until stiff, put some of it in a pouch to decorate and chill. Fold the berries into the rest of the mixture and spread the cream on the sponge cake plate. Roll up the sponge cake from the long side. Chill the roll for at least 2-3 hours.
Just before serving, decorate the roll with 12 dots of cream and put half a strawberry or a whole blackberry on top. Garnish with lemon balm.
Tip: The roll also tastes good with raspberries or blackberries, then use the appropriate type of yoghurt.
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