Though it's a drink you rarely think of 11 months of the year, there are a couple of reasons to do so. At the risk of upsetting Virginia: Egg Nog has arguably been a part of Christmas longer than Santa Claus. What's more, it was an important cocktail long before the Martini.
Some history is in order. Christmas was not always deemed an important holiday by Christians, nor was it necessarily celebrated. Theologically speaking, Easter is more important to the faith and therefore got top billing in the beginning. Christmas would come into its own later on. The Scriptures don't say much about the date of Jesus's birth, but 'round about the fourth century, leaders of the fledgling religion put it at December 25. Probably not coincidentally, that made it fall at the time of the Saturnalia, a pagan celebration of the winter solstice that wasn't politically correct anymore, but needed a replacement. After all, it's a pretty dark time of the year and the people needed a party.
In the meantime, there already was a Santa Claus. Nicholas was a bishop in the third century in what is now Turkey. Much like the jolly figure who comes down your chimney each year, he was known for his benevolence to children. His feast day was celebrated on December 6, however, not the 25th.
St. Nick and Christmas sailed along separately for hundreds of years. In the meantime, the latter became more and more a pagan celebration with attendant mischief, drinking and rioting. Indeed, revelry got so fierce that during the Protestant Reformation, attempts were made to outlaw the holiday altogether as heathen and anti-Christ. That wouldn't do, of course, and once the old nasties like Oliver Cromwell were out of power, the celebration came bobbing back to the surface. Praise to Jesus!
In the meantime, Egg Nog was evolving. The basic roots were drinks involving eggs (always), milk (usually) and some form of alcohol (which could vary widely from wine to beer to distilled spirits). The drinks developed in England, where also was invented the egg flip (a similar drink without milk). By the late 18th and early 19th centuries, egg nog was quite rightly associated with winter because of its fortifying properties in cold weather. And it was meant for really cold weather, not just a stiff breeze that might be taken care of with a stiff jolt of neat whiskey. Recipes for the Tom & Jerry (essentially a later variant of Egg Nog) specified that it should be drunk after the first snowfall.
Egg Nog was also a drink of the wealthy in England, as fewer people lived on farms or could afford milk. Therefore, it was a natural to give it to the less fortunate on Christmas as a way to demonstrate your charity.
As to the source of the name, many theories exist. Some have it that a nog, or noggin, was a cup for drinking the stuff. Others would argue that the term is a contraction of "egg and grog" (the latter word meaning rum). Nog is also a Brit slang for ale, and similar egg drinks have been made with brew instead of milk. Anyway, it's a pretty cool name that does the drink justice, especially if you've been hit on the noggin with a few before trying to wrap gifts or wrestle with a Christmas tree on Christmas Eve.
While it has its British roots, Egg Nog really came into its own in the New World, where the 17th century repression of Christmas festivities was still largely in force into the 19th century (the original Congress was in session on Christmas Day and you could get fined in Boston for celebrating). Egg Nog was a good way to put up some good ol' Christmas cheer without raising eyebrows.
It was also over here that rum became the liquor base of choice for the Egg Nog. After all, it was the favorite spirit of the colonies, so it was inevitable that it would make its way into the favorite punch. Yes, you buy Egg Nog in cartoons sans alcohol at the grocery store, but it isn't really Egg Nog until it gets liquored up. While brandy, Bourbon, and Scotch all make fine variations, with names like Kentucky Nog to show their spirit, Egg Nog with rum needs no special introduction.
In the meantime, what happened to old Saint Nick? Well, he didn't become Father Christmas in the western world until 1822 when Clement Clarke Moore wrote of him making such a clatter in his poem "A Visit from St. Nicholas" (a.k.a. "'Twas the Night Before Christmas"). Perhaps Santa was waiting for someone to leave out some good Egg Nog before making the Christmas visit a tradition. It was 40 years later when we got the current image of St. Nick as a portly gentleman via the cartoonist Thomas Nast, who also drew the robber barons of the day as obese. One guesses that the transformation of the image from a little sprite to the corpulent ho-ho-ho-ing Santa may have had something to do with the Egg Nog. There is no such thing as an Egg Nog diet and you can't help but be happy under its influence.
And as for the Martini: not invented until at least 1849 and probably not until the 1870s and even then not in its present form. Hardly the country's original American cocktail. Yes Virginia, there is a Santa Claus, but he drinks Egg Nog. So put away that shaker and get out a punch bowl. Here's a recipe:
6 eggs 1 cup sugar 1/2 teaspoon salt 1 cup spirits (as noted, whiskey and brandy work, but rum is traditional, preferably a fine aged rum like Bacardi 8 or Pampero.) 1 teaspoon vanilla 1 pint half and half cream 1 pint milk Nutmeg
In a large bowl, beat eggs to a froth. Add sugar and salt, continue beating. Stir in spirits, cream, vanilla and milk. Chill at least three hours (some recipes call for Egg Nog on the rocks, but our forefathers didn't have refrigerators.) Serve with a sprinkle of nutmeg.