Line a baking tray (approx. 35 x 40 cm) with baking paper. Separate the eggs. Beat the egg whites and 4 tbsp. cold water until stiff, adding salt and 125 g sugar. Beat the egg yolks separately into the mixture. Sift flour, starch and baking powder on top and fold in. Fold in brittle, except 1-2 tbsp. Spread on the baking tray. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/gas: level 3) for approx. 10 minutes
Turn onto a tea towel covered with 3 tablespoons of sugar, remove baking paper immediately. Stir 250 g jam until smooth, spread on the warm sponge cake. Cool down
Soak the gelatine in cold water. Whip 250 g cream until stiff. Mix quark, 75 g sugar and lemon peel. Squeeze the gelatine and dissolve over a mild heat
Stir in 3 tablespoons of lemon juice and then stir into the remaining juice. Stir into the quark mixture. Fold in the cream immediately and chill for approx. 10 minutes
Spread the quark cream on the sponge cake, leaving about 1 1/2 cm free all around. Roll up the sponge cake from the long side using the cloth. Chill for at least 4 hours, preferably overnight
Heat 3 tablespoons of jam, pass through a sieve. Cut lemon slices into corners. Whip 125 g cream until stiff. Cut roll into pieces. Decorate with icing sugar, cream, jam, lemon and the rest brittle