Separate the eggs, beat the egg whites until stiff, add 50 g sugar and salt at the end. Fold in 4 egg yolks one after the other. Add half the lemon peel. Sieve flour and starch onto the foam and fold in loosely.
Draw 6 circles (10-12 cm Ø) on a baking tray lined with baking paper. Spread the sponge cake mixture into the circles. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: not suitable/ gas: level 3) for 10-12 minutes.
Remove sponge omelettes immediately from the baking paper, fold them over a thin glass and let them cool down. Sort the blueberries, wash and drain. Whip cream, 25 g sugar, cream firming agent and remaining lemon peel until stiff.
Pour into a piping bag with a star-shaped spout and squirt the cream into the cooled omelettes. Press blueberries into the cream. Dust the omelettes with icing sugar and arrange them on a plate decorated with lemon slices and lemon balm.