Eggnog is a warming, spiced, creamy, and thick wintertime drink that combines milk, sugar, eggs, and alcohol. There are several theories about its origin, but the most probable claims that the combination of eggs and alcohol was an adaptation of posset—a hot drink made with spiced milk curdled with either ale or wine.
Some accounts claim that similar festive combinations of eggs and distilled spirits were prepared by monks. However, alcohol-laced milky drinks were likely enjoyed in various parts of medieval Europe, but that they were especially favored among the British aristocracy.
While the British would opt for sherry or brandy, the Americans would mostly lace their eggnog with rum or whiskey—since it was cheaper and more available. Traditionally, eggnog always included liquor (usually distilled spirit), eggs, and a hefty amount of spices, but contemporary variations are suitable for different adaptations, and may also be alcohol-free.
Similar milk-based drinks are also found in Mexico (rompope) and Puerto Rico (coquito). Eggnog is nowadays mostly enjoyed as a festive Christmastime drink. It can be served in glasses, mugs, or punch bowls. Although it is mostly enjoyed chilled, warm versions are also common.