Finely grind the nuts. Knead flour, sugar, fat, vanillin sugar, salt and egg to a smooth short pastry. Put in a cool place for about 30 minutes. Roll out the dough on a floured work surface to a circle (approx. 30 cm Ø) and put it into a greased springform pan (26 cm Ø), press the rim up about 2 cm.
Place baking paper on the dough, add peas and pre-bake in the preheated oven (electric cooker: 200°C/ gas: level 3) for 20-25 minutes. For the filling, drain mandarins well on a sieve.
Chop nuts. Put a tablespoon aside for decorating. Melt the fat and let it cool down. Separate eggs. Mix quark, egg yolk, lemon peel, 150 g sugar, remaining nuts and pudding powder. Beat the egg whites until stiff and gradually add the remaining sugar.
Carefully fold the egg white into the curd mixture. Fold in mandarins. Remove the base from the oven, remove the baking paper with the peas from the pan. Pour in the quark mixture, smooth it down and bake in the preheated oven (electric cooker: 175°C/ gas: level 2) for approx. 45 minutes.
Let the cake rest for about 5 minutes in the switched off oven. Place the cake on a cake rack, sprinkle with the nuts put aside and let it cool in the mould. Decorate the cake with sugar crystals and walnut halves.