Separate eggs. Beat the egg whites 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 and fold in. Line a baking tray (approx. 30 x 38 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: see manufacturer) for 8-10 minutes. Turn onto a tea towel sprinkled with a little sugar and carefully remove the baking paper. Roll up with the tea towel from the long side, allow to cool
Soak gelatine in cold water, squeeze it out and dissolve. Stir in 4 tablespoons of buttermilk, then stir into the remaining buttermilk. Chill buttermilk for 10-15 minutes until the mixture begins to gel
Meanwhile, wash 1 orange hot, rub dry and grate the peel thinly. Peel both oranges so that the white skin is completely removed. Remove the fillets with a sharp knife between the parting skins and let them drip off well in a sieve. Finely chop the chocolate coating. Whip the cream until stiff, while pouring in 50 g sugar. Fold yoghurt, orange fillets, orange peel and chocolate coating into the buttermilk mixture. Then carefully fold in the cream
Unroll the sponge cake and spread with buttermilk cream, leaving 1-2 cm of edge free on the upper long side. Roll up the sponge cake from the lower long side and chill for approx. 2 hours
Picture 02: Wash both oranges hot, grate dry and grate the peel thinly. Mix half of the orange peel into the buttermilk mixture, use the remaining orange peel for decoration
Preparation time 45-50 minutes. Waiting time approx. 2 hours