Frosted Ginger Cake with Crystallised Ginger

I was raised on ginger cake or gingerbread as we called it. It was a sticky dark cake that was baked in a bread tin or a big roasting tray and was particularly popular around bonfire night. This recipe is for a more elegant version which is pretty enough to grace any formal tea time table. You can make the cake and freeze it before frosting it, just defrost it overnight and then add the frosting the next day.