Roughly chop the chocolate and melt it in a bowl over a warm water bath. Melt butter in the chocolate. Beat the eggs and 150 g sugar with the whisk of the hand mixer for approx. 4 minutes
Mix flour, starch, cocoa and baking powder and alternately stir into the egg mixture with the chocolate butter mix. Pour the dough into a greased and flour-sprinkled springform pan (approx. 26 cm Ø) and bake in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for 35-45 minutes (stick test)
Take the cake out of the oven, loosen the edge and let it cool down on a cake rack. Carefully caramelise 150 g sugar in a wide saucepan. Add cream carefully and boil caramel for about 4 minutes at low heat while stirring. Remove caramel sauce from the stove and let it cool down a little
Coarsely chop the nut chocolate and add to the caramel sauce. Melt the chocolate while stirring. Let the chocolate-caramel sauce cool down. Remove the cake from the mould and pour the chocolate-caramel sauce over it
waiting time approx. 1 1/2 hours