I thought about this one deeply - it does not fit with UK, Scandinavian or Germanic traditions - but in Italy, they make a traditional sweet lemon liqueur called Limoncello.

Now, I can remember people "feeding" their christmas cakes with a tot of whisky or brandy a week when I was a child, so to feed a cake with a tot of limoncello a week might make sense from the aspect of an Italian version of a UK/French habit! Methinks the idea might have originated with the Normans - but they would use Calvados ...

People can buy 95% neat alcohol in Italy for making their own, and here is a US recipe

http://patty.vox.com/library/post/homemade-limoncello-when-life-gives-you-lemons.html

but there are lots of limoncello recipes on the www, if you search. And you can buy commercial versions in shops if you don't want to be bothered with the effort.

I'm pretty sure that was what your Dad was up to. Incidentally, did you know that "dad" is one of the few words that have passed into English from Romany?

LOL I'm a mine of interesting facts, and they want me to talk about cooking ...