Melt the butter. Put the biscuits in a freezer bag and crush them finely with a cake roll, mix with melted butter. Place a springform pan rim (26 cm Ø) on a cake plate. Pour the crumb mixture into the tin and press it firmly to a base. Put it in a cold place.
Mix quark, lemon juice, 75 g sugar and vanillin sugar until smooth. Stir in the sauce powder and cream firming agent. Whip 100 g cream until stiff. Cut balm leaves into fine strips and stir into the quark. Fold in the cream. Spread the quark mixture on the sponge cake base until smooth. Chill the cake for at least 2 hours. Whip the rest of the cream until stiff. Pour into a piping bag with star-shaped spout.
Spread the quark mixture on the sponge cake base until smooth. Chill the cake for at least 2 hours. Whip the rest of the cream until stiff. Pour into a piping bag with star-shaped spout. Loosen the edge of the springform pan and squirt small tuffs onto the cake. Decorate with lime slices, lemon balm and pistachios