Put flour, crumbled yeast, sugar, salt, egg and sour cream in a bowl. Warm the whipped cream slightly and melt the fat in it. Pour it into the bowl and work everything into a smooth dough using the dough hooks of the hand mixer.
Cover and leave to rise in a warm place for about 30 minutes until the dough has visibly increased in size. Meanwhile, cook a syrup from the sugar and 4 tablespoons of water at medium heat. Wash the apple, remove the core and grate roughly.
Finely dice the quince. Mix apple, quince, hazelnuts, almonds, jam, raisins and vanilla pulp with the syrup. Knead the yeast dough again well and roll out to a rectangle of 50x40 cm on a lightly floured work surface.
Spread the filling evenly on top, leaving a 2 cm margin all around. Fold in the sides and roll everything up. Then place on a baking tray lined with baking paper and leave to rise for another 15 minutes.
Spread the nut roll with whisked egg yolk and bake in the preheated oven (electric range: 175 °C/ gas: level 2) for 50-60 minutes. Then let it cool down on a cake rack. Serve with whipped cream as desired.
Results in about 40 slices.