Line a baking tray (approx. 35 x 40 cm) with baking paper. Preheat the oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Separate the eggs for the sponge cake. Beat the egg whites, 3 tbsp. cold water and 1 pinch of salt until stiff with the whisks of the mixer, adding 60 g sugar and 1 packet of vanilla sugar.
Fold in egg yolk. Mix flour and baking powder, sieve onto the egg mass and fold in.
Smooth the sponge mixture onto the baking tray. Bake in a hot oven for about 8 minutes until golden brown. Moisten a tea towel and sprinkle with some sugar. Take out the sponge cake, loosen it from the edge and fall onto the tea towel.
Carefully remove the baking paper. Place the dish cloth over the sponge cake and let it cool down.
For the cream, soak gelatine in cold water. Mix the quark, 2 tablespoons of sugar and lemon rind. Squeeze the gelatine, dissolve in a small pot at very low heat. First stir in 2 tbsp. quark, then stir everything into the rest of the quark cream.
Chill for about 10 minutes until the cream begins to gel.
Remove 2 tablespoons of the fruit spread and set aside. Spread the rest on the sponge cake, leaving an approx. 2 cm wide rim. Whip 100 g cream until stiff, fold it into the quark cream and spread it on the fruit spread.
Roll up the sponge cake from a short side, cover and chill for about 2 hours.
Select the berries, wash if necessary and dab dry well. Clean the strawberries and cut them into pieces. Strip currants from the panicles. Mix the remaining fruit spread, 1-2 tbsp. sugar and lemon juice.
Mix carefully with the berries.
Whip 200 g cream until stiff and pour in 1 vanilla sugar. Cut the sponge roll into 8-9 thick slices (3.5-4 cm each) and tilt them so that the slices lie on the cut surface.
Spread cream on the top and sides of the slices and place on a cake plate. Spread the berries on the tartlets just before serving.