Separate eggs, beat egg whites and 1 tablespoon of lukewarm water until stiff. Add sugar and vanillin sugar. Stir in the whole egg yolk bit by bit. Mix flour, cocoa and baking powder and sieve onto the egg foam.
Stir in loosely. Spread the mixture on a baking tray lined with baking paper. Bake in a preheated oven (electric: 200 °C/ gas: level 3) for about 10 minutes. Turn out onto a damp tea towel sprinkled with sugar.
Peel off the baking parchment and whip the tea towel over the sponge cake and let it cool down. Soak the gelatine in cold water. Carefully wash the strawberries, dab them dry and, except for about 250 g for decoration, clean them.
Puree 200 g strawberries and jam. Squeeze the gelatine, dissolve and stir into the puree. Chill for a short time until the mixture begins to gel. In the meantime, cut 300 g strawberries into cubes.
Whip 200 g cream until stiff. Fold cream, strawberries and lemon peel into the puree. Spread evenly on the sponge cake and roll up. Chill for about 1 hour. Halve the remaining strawberries. Melt the chocolate coating.
Whip the remaining cream and sugar until stiff. Spread the sponge roll with cream. Pour the chocolate coating into a freezer bag, cut off a small corner and spray strips over the roll. Decorate with strawberries and keep cool until serving.
Results in about 18 slices.