I make it too - I buy a bottle of brandy that I use when I make the cake and the pudding (though I don't make a pudding every year). After Christmas it comes in handy from time to time in cooking.
Brandy butter recipe:
I'm not sure of the amounts, but you start with a lump of softened butter - probably about 75g. into which you beat sugar - I use caster because I like the slight crunch it gives, but some people use icing sugar. When you've beaten some sugar into the butter, and it looks like brandy butter, gradually add the brandy, probably at a teaspoon a time, beating it in and tasting as you go, until it's the strength you want it - you may have to add a bit of extra sugar if it gets too wet.
I suppose it's not as much a recipe as a set of three ingredients that you combine in amounts to suit you.
Merry Christmas!
sunnygirl.