Chop cashews. Mix 250 g flour, 100 g sugar, 175 g butter in pieces and cashew nuts with your hands to form crumbles. Chill the crumbles for about 30 minutes
In the meantime, chop the chocolate and melt it over a warm water bath. Take it off and let it cool down a little. Cream 80 g butter, 70 g sugar, vanilla sugar and salt with the whisk of the hand mixer. Stir in the eggs one after the other. Mix 80 g flour, baking powder and cocoa powder. First stir liquid chocolate, then flour mixture into the egg mixture. Pour the dough into a greased springform pan (24 cm Ø) sprinkled with flour and bake in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 10 minutes
Wash the nectarines, carefully rub dry, cut in half, remove stones. Cut halves into slices. Take the cake out of the oven, carefully put jam on the dough. Spread nectarine slices and crumbles on top. Put the cake back into the oven and bake at the same temperature for 30-35 minutes. Remove from the oven and allow to cool on a cake rack