Cut the nougat into cubes. Cream butter, 150 g sugar, vanillin sugar and salt with the whisk of the hand mixer. Alternately stir in eggs and 25 g starch. Add 125 g quark and stir in.
Mix flour, 50 g starch, baking powder and hazelnuts, stir in briefly. Fold in nougat cubes.
Put the dough into a greased, breadcrumbed box cake tin (30 cm long, 11 cm wide, approx. 1.8 litres capacity) and smooth it down. In a preheated oven, 2nd rail from below (electric cooker: 175 °C/ circulating air: 150 °C/ gas: see
manufacturer) bake for about 1 hour. Let the cake cool down on a cake rack for about 30 minutes, then carefully remove it from the edge of the tin, turn it over onto a plate and let it cool down for about 2 hours.
In the meantime peel the apple, quarter it and cut out the core. Cut the quarter into small pieces. Sprinkle with lemon juice. Mix mascarpone, 60 g quark and 50 g sugar. Fold in apple pieces.
Cut the cake horizontally. Spread the mascarpone cream on the lower cake base, place the upper cake base on top.
Roughly chop the chocolate and melt over a warm water bath. Allow to cool slightly and spread on the cake in waves. Chill the cake.