Beat the eggs, yolks, sugar and vanilla sugar over a saucepan of boiling water till the mixture is warm and fluffy. Place the bowl in cold water and continue beating until the mixture has cooled down again. Carefully fold in the sifted flour and then the melted butter. Immediately spread on to a baking parchment lined baking sheet and bake for approximately 10 minutes at 200°C.
Sprinkle a clean tea towel with sugar and turn the sponge out onto it. Immediately roll it up using the cloth and leave to cool.
For the filling, purèe half the strawberries and cut the rest into pieces. Whip the cream with the sugar until stiff, fold half into the strawberry pulp and chill the rest.
Unroll the sponge and spread with the strawberry cream mixture. Sprinkle the small strawberry pieces over it and roll the sponge back up again. Spread the remaining cream over the swiss roll and add some cream rosettes using a piping bag. Decorate with strawberry and serve chilled if possible.