Chocolate Pistachio Orange Cake

This is one of my favourite cakes, bar none. I first prepared it for a lunch cooked by my friend Ann Amendolara Nurse at the James Beard House in New York in the autumn of 1988. A restaurant chef had cancelled at the last minute and Ann was called in to replace him for one in a series of Italian lunches. The first thing Ann did was to phone and ask me to make a dessert and this