Beat the egg yolks with the sugar to a smooth cream. Add the flour, grated lemon rind and a little cognac, if you like, for a more pleasant aroma.
Separately, beat the whites with a pinch of salt and carefully stir with the remaining mixture. Pour the mixture into a rectangular tray laid out with slightly oiled baking paper.
Bake the cake layer in a preheated oven until ready. After cooling, cut it into 1-3 more layers, then stick together with a suitable cream.