Rich Chocolate Cake with Chocolate Sauce

If you ever get a chocolate urge, then this chocolate cake will satisfy it. It is known in the Italian Jewish community as torta Susanna; who Susanna is or was is still a mystery... but she was definitely a great baker! It has always been a classic in our family in Rome, where we often serve it cold from the fridge with whipped cream, and it is also a classic in my family in London, where we are far less patient, so we often end up eating it shortly after it comes out of the oven,