Fernet takes us behind the bar at Harold's Bayonet Room

When Colorado booze manages to infiltrate the secretive San Francisco market, it's time to take notice. A recent trip to the Other Queen City found bottles of Leopold Bros. Highland Amaro Fernet being downed. This, in a place where Fernet Branca, the leading manufacturer of the bitter-tasting stuff, draws 40 percent of its U.S. sales.

People have been calling Fernet -- a thick herbal liqueur recipe originally of Italian extraction -- a fad for more than a decade ago. By the time you read this, approximately 276,000 think-pieces on Fernet's popularity will have been published, all pondering the reason a liquid secret handshake among bartenders has infiltrated pop culture. With some help from the fine folk at Harold's and the Bayonet Room in Longmont, I found the answer.

See also: Going beyond white lightning at Boulder Distillery

Bartenders are the movie stars of the service industry -- always visible and dependent on the good will of their fans -- so why wouldn't we want to emulate them? Aside from the back aches and liver problems, of course. So when word got around that barkeeps were trading shots of Fernet in some sort of weird bar ritual, everyone wanted to see what the fuss was about.

"We love Fernet, we love to drink Fernet at the bar. Using it in a cocktail is a good reason to keep it here," says Natasha Kramlich, bar manager at Harold's. And that cocktail is the Fernet Flip ($9), a dark and stormy blast of herbal flavor that doubles down on Fernet Branca's inherent muskiness. With the herbal vermouth Carpani Antica, coffee liqueur, housemade bitters and a whole egg for creaminess, this flip is like a prep-table dare that somehow got on the menu. And it can be a tough sell in Longmont, not usually known as a bastion of mixology.

"We often have to educate a lot of people who come in here. It's often not the same crowd as you get at theBitter Bar or Williams & Graham," says Jonathan William, assistant manager. But with a heavenly halo of spicy foam and a serious herb punch, the Fernet Flip is an education just on its own.

Of the dozens of Fernet Flip recipes floating about, the only mandatory ingredients are Carpani and egg, so use Harold's version as a jumping-off point. Pass this drink around and you might make some new friends -- or lose them forever. Hey, it's the industry, right?

Basic Fernet Flip Ingredients:

1.5 oz. Fernet (Fernet Branca or Leopold Bros.) 1.5 oz. Carpani Antica vermouth 1 oz. simple syrup dash Angostura bitters (or other variety) 1 whole egg

Combine ingredients in a cocktail shaker, including egg. Give mixture one stir, then add ice. Shake like hell until egg is separated with other ingredients and foamy. Strain into chilled old-fashioned glass. Congrats--you're officially sophisticated. Your Warby Parker glasses and Belle and Sebastian records will be in the mail any day now.

With every installment of Coming of Age with 21 Drinks, I'll be featuring a cocktail recipe cooked up by me or the bar itself. Have a suggestion for a place I should visit? Post it below.