This cake is magnificent in its damp blackness. I can't say that you can absolutely taste the stout in it, but there is certainly a resonant, ferrous tang which I happen to love. The best way of describing it is to say that it's like gingerbread without the spices. There is enough sugar — a certain understatement here — to counter any potential bitterness of the Guinness, and although I've eaten versions of this made up like a chocolate sandwich cake, stuffed and slathered in a rich chocolate icing, I think that can take away from its dark majesty. Besides, I wanted to make a cream cheese frosting to echo the pale head that sits on top of a glass of stout. It's unconventional to add cream but it makes it frothier and lighter which I regard as aesthetically and gastronomically desirable. But it is perfectly acceptable to leave the cake un-iced: in fact, it tastes gorgeous plain. For US cup measures, use the toggle at the top of the ingredients list.