Line 2 baking trays with baking paper and draw 4 circles (each approx. 12 cm Ø). Separate the eggs. Beat egg white and salt until stiff, add sugar and 1 vanillin sugar. Sift flour and starch into the mixture and fold in. Spread half the sponge cake on 4 marked circles. Bake in the preheated oven (electric cooker: 200 °C/circulating air: 175 °C/gas: level 3) for approx. 10 minutes
In the meantime, spread the remaining biscuit on the circles of the 2nd tray. Bake in the same way. Remove the baked omelettes immediately from the baking paper. Fold them over and put a small roll of aluminium foil between each of them and let them cool down
Break the chocolate into pieces and melt in a hot water bath. Pour into a plastic bag and cut off a small corner. Decorate the omelets with chocolate strips. Leave to dry
Whip the cream until stiff, adding cream firming agent and 1 vanilla sugar. Fold in lemon zest. Pour into a piping bag with star-shaped spout. Remove the aluminium rolls. Fill the omelettes with the cream. Decorate with icing sugar, lemon corners and lemon balm