Separate the eggs for the biscuit. Beat the egg whites until stiff. Sprinkle in the salt and 100 g sugar. Add the egg yolks and stir in. Mix the flour and baking powder, sieve into the egg mixture and fold in.
Place the dough on a baking sheet lined with baking paper and smooth it out. Bake in a preheated oven at 175 ° C (convection) for 10 - 12 minutes. Then turn out onto a damp tea towel sprinkled with sugar. Carefully peel off the baking paper and carefully roll up the cake with the towel. Let cool down.
Soak the gelatine in water for the filling. Mix together yogurt, quark, 75 g sugar, lemon zest and lemon juice. Squeeze out the gelatine and dissolve it carefully. Stir some cream into the gelatin, then stir everything under the rest of the cream. Chill for about 5 minutes until the cream begins to gel. Whip 150 g cream until stiff and fold into the cream.
Roll out the sponge cake again. Spread the cream on the plate, roll up again and refrigerate for at least 3 hours. Whip the rest of the cream until stiff and decorate with cream tuffs, lemon balm and lemons.