A good, high end bourbon, but only enough to add a subtle nuance to the nutmeg/clove spiciness. The equivalent of maybe a quarter of a shot per serving. Not enough to catch a buzz.
Now is a great time to make your aged eggnog with sufficient maturation time for Christmas. See Alton Brown recipe widely available on the internets.
I still have a jar in the fridge from last year. It should be delicious now. @eriner
@Richard Without strong brandy it's basically a sweet mayonaise.
Booze reduces the caloric intake by at least half.