Preheat oven to 180 C / Gas 4. Line a deep baking tin with greaseproof paper.
In a bowl beat egg yolks with lemon zest until light and creamy. Gradually add 2/3 of the sugar. In a separate bowl beat egg whites with 4 tablespoons water and salt until stiff. Whisk in the remaining sugar. Fold the stiff egg whites into the egg yolk mixture.
Sift flour, starch and baking powder over the egg mixture and fold in carefully.
Pour dough into the prepared baking tin. Bake for 5 minutes, then reduce the temperature to 120 C / Gas 1-2 and bake for a further 10 minutes.
Meanwhile wash and dry raspberries.
Sprinkle a clean kitchen towel with sugar and turn baked biscuit on it. Peel off greaseproof paper and roll up biscuit whilst still warm. Let cool.
To make the filling, beat whipped cream with vanilla sugar until stiff. In a separate bowl mix raspberries with sugar to taste and stir in a dash of lemon juice. Fold into the whipped cream.
Carefully unroll biscuit and spread the raspberry cream evenly on top. Roll back up and place onto a cake platter. Cover and chill for a few hours in the fridge.