Oh my! Grans to the rescue it is! Well... not to the recipe I forgot about (more on that later) but loads of yummy ideas. Thank you all.
I'm intrigued by the Indian Black Cake idea. The Scots have something called Black Bun that is solid, compacted dried fruit wrapped in firm pastry. Some recipes have brandy in them and it is usually eaten with a nip of whisky at Hogmanay.
They say that a problem shared is a problem halved. Well, once I'd posted the OP it somehow occurred to me to open an ancient notebook of mine into which I've jotted recipes over the years. It's chockablock now. And guess what, I'd bookmarked a recipe for Nigella Lawson's carrot and almond cake from years ago which contains some rum.
So my brain was working after all.... kinda ?
Thanks again for the ideas. They should keep me busy. Told MrB about this thread and he's very keen that I experiment with all your ideas.