Beat the fat and 300 g sugar with the whisk of the hand mixer until foamy. Stir in the eggs one after the other. Mix flour, buckwheat flour and baking powder and stir in by the spoonful. Halve the dough. Put some hazelnuts aside and roughly chop the rest.
Mix one half of the dough with cocoa and chopped hazelnuts. Put some cranberries aside for decoration. Dust the rest with flour and fold into the other half of the dough. Grease a box form (24 x 11 cm; 1.5 litres capacity) and sprinkle a thin layer of breadcrumbs over it. Fill in the dough alternately by the spoonful and use a fork to draw streaks. Bake in the preheated oven (electric range: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 90 minutes. Let rest for 10 minutes. Turn out of the tin and let it cool down on a cake rack. In the meantime, melt 30 g sugar in a pan. Add the hazelnuts and caramelise.
Bake in the preheated oven (electric range: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 90 minutes. Let rest for 10 minutes. Turn out of the tin and let it cool down on a cake rack. In the meantime, melt 30 g sugar in a pan. Add the hazelnuts and caramelise. Put them on aluminium foil and let them get firm. Dust the cake with a little icing sugar and decorate with caramelized hazelnuts, crème fraîche and the remaining cranberries