For the sponge cake roulade, mix the powdered sugar, yolks and the grated zest of the lemon until the mixture is light in color.
Beat egg whites, salt and baking powder together until stiff, add fine crystal sugar and snow and continue beating briefly. Carefully fold in flour.
Liquefy butter and let cool, stir into the mass. Spread the mixture on a baking tray lined with baking paper.
Bake the sponge cake in a preheated oven at 240 degrees for about 5 minutes. Then turn the sponge out onto a damp tea towel, sprinkle the paper with water and carefully peel off the baking paper.
For the filling, cream the butter until fluffy. Add the powdered sugar, two yolks and the grated lemon zest. Finally, carefully stir in the lemon juice until a smooth mixture is formed.
Spread the cream on the finished sponge cake, roll it up and put it in a cool place.