Roughly dice the nut nougat and melt in a water bath. In the meantime crumble the rusks finely. Mix melted nougat, rusk crumbs and bitter almond flavour. Line a springform pan (26 cm Ø) with baking paper.
Pour the rusk nougat mixture onto the bottom of the springform pan and press down. Put the base in a cool place for about 1/2 hour. Meanwhile, drain mandarins well on a sieve, catching the juice. Soak gelatine in cold water.
Mix curd, sugar, vanilla sugar, lime juice, liqueur, 75 ml tangerine juice and 1/2 of the tangerines well with the whisks of the hand mixer. Whip the cream until stiff. Squeeze out the gelatine and melt in a small pot at low heat.
Mix droplets into the curd mixture while stirring continuously (with a hand mixer). Add half of the remaining mandarins. Chill the quark mixture for approx. 4 minutes. When it begins to gel, fold in the cream in portions.
Pour the curd and mandarin mixture onto the base. Put the cake in a cool place for about 3 hours. Remove from the mould and place on a cake plate. Sprinkle the cake with the remaining mandarins and serve decorated as desired with lime zest, slices and lemon balm.