Separate the eggs, beat the yolks with sugar, vanilla sugar and hot water for about 15 minutes until very creamy. Mix the flour, baking powder and cocoa in a separate bowl and sift into the egg yolk cream by tablespoon, fold in loosely. Beat the egg whites until stiff and fold in, quickly pour onto a flat tray lined with baking paper, smooth out and bake at 190 ° C for about 10 minutes. The parchment paper must be larger than the baking sheet so that there is an edge.
Immediately after baking, turn it out onto a sugar-sprinkled cloth, roll it up loosely and let it cool. Unroll again before covering.
Drain the sour creams (put a few nice ones aside) and spread them on the dough. Whip the cream with icing sugar and cream stiffener and spread about half of it evenly over the cherries. Roll up, brush the roll with cream and put the last of the cream into a piping bag.
Decorate with cream and cherries, sprinkle with chocolate sprinkles if desired.
Tip: You can also form a Danube wave roll, i.e. replace the cream with a buttercream made from vanilla pudding and 250 g butter.