Line a baking tray (approx. 35 x 40 cm) with baking paper. Separate the eggs. Beat the egg whites until stiff, while pouring in 120 g sugar. Beat the egg yolks into the mixture one after the other. Mix flour, starch and baking powder, sieve and fold in
Spread the sponge cake on the baking tray. Bake in the preheated oven (electric cooker: 200 °C / convection oven: 175 °C / gas: level 3) for about 12 minutes
Turn onto a tea towel sprinkled with 2 tablespoons of sugar. Remove baking paper immediately. Roll up the sponge cake together with the tea towel and let it cool down
Clean, wash and chop the rhubarb. Steam in 3-4 tablespoons of water and 30 g of sugar covered for about 6 minutes and let it cool down. Wash and clean the strawberries
Puree 1/3 strawberries and 1/3 rhubarb together. Dice the rest of the strawberries
Whip the cream until stiff, adding cream firming agent and vanillin sugar. Stir strawberry-rhubarb puree and the rest of the rhubarb into the quark. Fold the cream first and then the strawberry cubes into the quark
Unroll the sponge cake. Spread the quark cream on it and roll it up. Chill for about 2 hours. Dust with icing sugar and decorate if necessary