A Tom and Jerry is a classic Christmastime cocktail in the United States. It is a version of Eggnog with brandy and rum added and served hot, usually in a mug or a bowl. The main difference between Tom & Jerry and the Eggnog is that the first is served warm, and the Eggnog, on the other hand, is cold and already mixed and ready to drink. It’s a sweet, warm drink flavored with dark rum and cognac, and it’s been a holiday choice since the 1820s, particularly in the Midwest.