It must be the festive season that's put me in a citrus mood. And it can't be helped, really, since everywhere you turn there are kumquats and mandarins, satsumas and oranges galore. So for dessert over many festive dinners, our table has been laden with all things orange. At one dinner was crepes with kumquat compote and vanilla ice cream; at another was our nostalgic orange trifle which my…