Sponge: Whisk egg yolks with the lemon zest until foamy and gradually add in 2/3 of the sugar. Whisk the egg whites with 4 tablespoons of cold water and salt until stiff then gradually add the rest of the sugar. Fold the egg whites into the egg yolks.
Sieve the flour, cornflour and baking powder into a bowl then fold in the egg mixture.
Preheat the oven to 160 degrees. Line a deep baking tin with baking paper and spread the dough evenly over it.
Bake in the preheated oven for 15 minutes.
Sprinkle a tea towel with the sugar and flip the finished sponge onto it. Remove the baking paper and roll up the sponge while still warm then allow to cool.
Filling: Set 8-10 strawberries aside for the decoration; wash and dice the others. Marinade in a bowl with sugar and lemon juice.
Whisk the cream with the vanilla.
Unroll the sponge carefully and spread the jam over it. Then a apply a layer of whipped cream and finally spread the marinated strawberries over it.
Carefully roll up the sponge again. Place the Swiss roll on a plate with the seam down and cover with the remaining cream. Garnish with some strawberry halves or whole strawberries.