Separate eggs. Beat the egg white until stiff, add 75 g sugar and salt. Stir in egg yolks one after the other. Mix flour, cocoa and baking powder, sieve over the egg mixture. Fold in together with the milk.
Line a baking tray (approx. 32 x 39 cm) with baking paper. Spread the mixture evenly on top. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 10 minutes. Turn over onto a tea towel sprinkled with sugar, carefully remove the baking paper, turn the sponge cake plate over again. Roll up from a narrow side with the tea towel, allow to cool
Soak the gelatine. Peel clementines and divide into segments. Mix quark, yoghurt, 50 g sugar, vanillin sugar and lemon juice. Heat 1-2 tbsp. quark mixture, dissolve gelatine in it and stir everything back into the remaining quark mixture. As soon as the cream starts to gel, whip 100 g cream until stiff, fold in
Unroll the sponge cake plate again. Pour cream on top, spread, leaving an approx. 1 cm wide edge free. Place about 3/4 of the clementine pieces next to each other on top. Roll up the sponge cake firmly and chill for 2-3 hours.
Shortly before serving, whip 200 g of cream until stiff, fill into a piping bag with a large perforated spout. Dust the roll first with icing sugar, then in places with cocoa. Decorate with cream and remaining clementines
waiting time approx. 3 hours