Dairy is a natural companion to the richness of an egg. Either can contribute to the texture of a cocktail in a dramatic way, and when they’re combined the effect is amplified. Of course, Eggnog is the classic example. Though it’s typically made in large batches that involve a lot of work—preparing a custard base and then spiking it with booze—that isn’t always convenient (and never quick), so we’ve come up with this single-serving version of Eggnog that can be made à la minute and without much prep.