Liquor is optional? Bwahahahaaaaa! No, seriously, my first thought upon reading this recipe was, "Hmmm... I'll bet it would be nice to use with hot cider (not necessarily 'hard' cider) instead of water or milk." I confess to a fondness for dark rum, so I'd probably try it that way first. If one does choose to make it with rum I'd suggest using no more than two shots per mug; one may be plenty for your taste. Then fill with hot water. Another option (if you like the rum flavor but not the alcohol) is to use a bit of pure rum extract. Careful, it won't take much to get the flavor. I'd start with 1 teaspoon and work from there.