Beat the eggs, sugar and lemon zest with the whisk of the hand mixer until foamy (the sugar must be dissolved). Sift the flour and starch over the mixture and fold in with the whisk. Grease the baking tray, line it with parchment paper and spread the sponge cake mixture on top. Bake in a preheated oven (electric: 200 °C/ gas: level 3) for 10-12 minutes until golden brown.
In the meantime, moisten a kitchen towel and sprinkle thinly with sugar. Turn the sponge plate over and remove the paper immediately. Roll up the base with the kitchen towel. Let it cool down
For the filling, sprinkle the frozen blueberries with 1 tablespoon of sugar, soak. Soak the gelatine in cold water. Mix quark, lemon juice, vanillin sugar and remaining sugar. Squeeze the gelatine, dissolve carefully
Stir into the curd. Cool until it begins to become greasy. In the meantime whip the cream until stiff. Carefully fold the cream and blueberries into the quark. Roll off the sponge roll again and spread with the quark cream. Roll up, press down lightly. Arrange on a cake plate. Dust with icing sugar. Decorate with mint and lemon peel as desired. Results in about 16 slices