SAN FRANCISCO — At Scoma’s Restaurant in San Francisco, this holiday season’s batch of eggnog began 11 months ago.

The process typically starts in late January, just after the previous year’s celebrations are over. Nearly a thousand egg yolks, gallons upon gallons of heavy cream and roughly $1,000 worth of vanilla beans are mixed with sugar and a mega-cocktail of sherry, brandy and aged rum. The concoction is then stored at 34 degrees Fahrenheit (1 degree Celsius) and and gets stirred weekly for months.

Is it worth the wait? Customer Phil Kenny seems to think so.

“It’s a wonderful, specialty drink,” Kenny said of Scoma’s recipe, which has been honed in recent years to take advantage of the boozy beverage’s aging process. “This takes eggnog to a different level.”

Kenny and his wife, Laurie, aren’t the only ones enjoying it this year.

“A drink that you would sort of associate with grandma and grandpa on the holidays has become like a cult favorite here,” Gordon Drysdale, Scoma’s culinary director, said earlier this month. “We did not ever anticipate people actually being mad at us because we didn’t have it.”

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Eggnog’s Medieval Origins

Eggnog’s roots date back to medieval England and a drink called “posset,” which included hot milk or cream, alcohol and spices. Recipes have evolved in the centuries since then, and non-dairy and alcohol-free options abound in recent years. But some — like the formula for the famous eggnog daiquiri at Lafitte’s Blacksmith Shop in New Orleans — stay the same, and remain secret.

“I like to say it’s a little Christmas magic,” said Jamie Gourges, marketing manager for the open-air bar in the city’s iconic French Quarter. “We do not disclose any of our recipes at any point but it is delicious.”

Gourges will say, though, that theirs is made fresh each morning from right after Thanksgiving until Three Kings Day, also known as Epiphany, on Jan. 6. It’s a tradition going back some 20 years at an establishment that was built in the early 1700s. Naturally, it’s haunted by French pirate and privateer Jean Lafitte, who based his smuggling operations near New Orleans.

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A Holiday Favorite in the Big Easy

Terry Wittmer, who lives in the Big Easy, is a regular customer and loves the holiday season at the bar.

“It tastes like Christmas. It’s a little cinnamon-y. It’s smooth and if you drink it too fast you might get a brain freeze,” Wittmer said. “I live a block away so I’m here every day but I’m happier during Christmas.”

Even for tourists who came for the bar’s signature “purple drank” daiquiri, the holiday beverage beckons.

“It’s not going to have a problem going down, let’s put it that way,” Cheryl Abrigo of Florida said as she sipped hers.