The last time a barfly ordered a Mule’s Hind Leg or a Fluffy Ruffle was likely when Harry Craddock was still behind the American Bar at London’s Savoy Hotel in the ‘20s. Craddock compiled the legendary “Savoy Cocktail Book,”  published in 1930, containing hundreds of recipes. Like the two above, many have not been embraced by contemporary drinkers. But one recipe is among the most well-known classic cocktails of all time and remains popular to this day: the Corpse Reviver #2.

The Corpse Reviver’s recipe is simple. Four common ingredients (gin, Lillet or Cocchi Americano, Cointreau, and lemon juice), all in equal proportions, seasoned with a spritz of absinthe, adding up to that three-ounce magic number.

The four-equal-part formula crops up often in the cocktail world. It is found in other resurgent classics like the Last Word (gin, green Chartreuse, Maraschino liqueur, and lime juice) and modern riffs like Sam Ross’s Paper Plane (bourbon, Aperol, Amaro Nonino, and lemon juice) and Joaquín Simó’s Naked and Famous (mezcal, yellow Chartreuse, Aperol, and lime juice), which have gone on to become contemporary classics in their own right.

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So what is it about this versatile formula that keeps bartenders and barflies coming back?

You Never Have to Flip Your Jigger

The obvious appeal of the equal-part formula is ease. Not only is it simple to remember, but the four recipes above feature ingredients that are easy to find and use. The result is a seemingly foolproof spec for generating classic drinks with staying power.

“Classics remain classics for a reason,” says Pippa Guy, ambassador for Tanqueray No. Ten, Diageo World Class, and formerly the first female senior bartender at the Savoy’s American Bar since Ada Coleman more than 100 years ago. “Simple formulas, ease of access to ingredients on any back bar the world over, and versatility within the formula for delicious twists.”

“You never have to flip your jigger,” adds Joaquín Simó, a drinks consultant who invented the Naked and Famous in 2011 while bartending at New York City’s Death & Co.

The simplicity also gives these drinks reach, an attractive quality for ambitious bartenders looking to make a name for themselves. What better way to get their name out there than by attaching it to a recipe that can be made at any bar in the world?

“You don’t have to publish it in a book with the recipes for your house infusions, you just put it out there and it spreads like fire,” says Brandon Ravare, beverage manager at the Los Angeles Athletic Club.

But mastering the four-equal-part formula and its challenges is easier said than done.

A Balancing Act

Balance is everything in cocktail creation and the four-equal-part formula puts this on display. Rather than a base spirit giving the drink most of its structure, the spec leans on two liqueurs that take up twice the total volume in the drink compared to the base while also acting as the drink’s sweetener.

“It’s not forgiving,” says Simó. “Understanding the role that sugar is playing in that weirdly constructed drink is super important if you’re going to get it.”

Many people think sugar only makes things sweet, but it is a crucial ingredient that adds body, mouthfeel, and viscosity to a cocktail. The deceptive sweetness of many liqueurs makes them harder to balance, like the bitter-tasting but sugar-loaded Campari. “There’s a reason why pastry chef’s love it,” Simó says.

Liqueurs do have one advantage: alcohol. The drying aspect that alcohol brings allows for more complexity and depth in drink construction.

“You’re able to layer flavors upon flavors more than if you were using traditional sweeteners like simple syrup, honey, or orgeat,” says Sam Ross, bartender and co-owner of New York City’s Temple Bar and Attaboy, as well as Attaboy in Nashville.

On paper, the eye-catching mix of polarizing ingredients seems impossible to balance. “You might be quick to dismiss it,” Ross adds. “Then you shake up this amazing combination that you never knew existed and you tip your cap.”

But for the four most famous equal-parts drinks, balancing the formula is just part of their journey to becoming classics.

The Everlasting Word

Invented around 1910 at the Detroit Athletic Club, the aptly named Last Word became a statement of the cocktail resurgence of the 2000s after being rediscovered and popularized at Seattle’s Zig Zag Café by Murray Stenson.

“It became one of the secret handshake cocktails where you walked into a bar and if they knew what it was, had the ingredients, and could make you a good version, then you knew you were in a great bar,” says Simó.

The sophisticated recipe came back at a time when cocktails were being reexamined as a culinary experience — the century-old Last Word showing that, far from being a contemporary notion, the link between gastronomy and cocktail culture has deep roots. “It’s actually a very historic, and very American, idea,” says Ravare.

Perhaps the most significant legacy of the Last Word is how it elevated one of its key ingredients: Maraschino liqueur.

“For me, drink creation is more of an organic process, but the Paper Plane was very intentional. It was so delicious that I wanted to showcase it, and what better way than to use the Last Word formula.”

“At first only Luxardo was available,” says Max Seaman, sommelier at Republique in Los Angeles and former longtime manager of iconic craft cocktail bar The Varnish. That changed as the cocktail renaissance grew along with the popularity of the Last Word. “All these other products became available, like Maraska, which we swore by.”

A Revival Story

After Prohibition and the drink-making dark ages of the ‘70s and ‘80s killed cocktail culture in America, even the delicious and deceptively complex Corpse Reviver #2 needed reviving. The renewed interest in craft, led by bartenders like Dale Degroff and Sasha Petraske, brought many classic recipes back from extinction. But there is something the Corpse Reviver #2 has alongside great flavor and a formula that stands out: a great story.

“It helped that it had a catchy quote attached to it,” says Leandro Monriva, co-creator and host of The Educated Barfly, a YouTube channel specializing in cocktail tutorials using professional technique. The quote from Harry Craddock, printed next to the recipe in the “Savoy Cocktail Book,” cautions that “four taken in quick succession will un-revive the corpse again.”

There is a legend that Craddock, an icon of cocktail lore in his own right, buried a Corpse Reviver in a shaker in the walls of the American Bar. The story goes that Savoy bartender Peter Dorelli found the shaker during a renovation and reburied it.

“He’ll neither confirm nor deny,” says Guy of her former colleague. But the tale lives on, and so does the drink. “It’s about something being memorable, the tongue-in-cheek name, and the fact that people can enjoy it, to this day, in its home,” she says. When a cocktail captivates the imagination, as the Corpse Reviver does, it becomes immortal.

A Drink and a Song

It reads like a recipe you might find buried in the “Savoy Cocktail Book” — the presence of Amaro Nonino gives it an old-world vibe — but the Paper Plane is not an old drink. Sam Ross invented it in 2007 while working at Sasha Petraske’s legendary Milk & Honey in New York. Though he rarely sets out to invent a drink in advance, Ross jumped at the chance to do so for the first summer menu of Chicago’s Violet Hour.

“Drinks that have a narrative arc to them, a beginning, middle, and end, where there’s movement, and there’s change happening, that’s what you keep going back to.”

“For me, drink creation is more of an organic process, but the Paper Plane was very intentional,” Ross says. There were two specific inspirations he had for the cocktail: the new-to-America Amaro Nonino, and the four-equal-part spec. “It was so delicious that I wanted to showcase it, and what better way than to use the Last Word formula.”

Amaro Nonino was not only the secret sauce of the recipe, but a big part of the drink’s legacy. At the time Ross created the cocktail, amari were not popular in the U.S. The Paper Plane helped change that. “That drink really normalized the use of amari in American bartending,” says Monriva.

But where did that seemingly timeless name come from?

“He would not stop playing that new M.I.A. album during setup and breakdown,” says Simó, recounting nights spent visiting Ross at Milk & Honey at the time. It was only fitting that one of the songs should name the drink.

Naked and World Famous

The Naked and Famous proves that a good story can make a drink famous. In the case of Joaquín Simó’s cocktail, that story is told entirely with flavor.

“Drinks that have a narrative arc to them, a beginning, middle, and end, where there’s movement, and there’s change happening,” he says, “that’s what you keep going back to.”

The journey of the Naked and Famous started while Simó was working under Phil Ward at Death & Co. After watching Ward successfully swap the gin and lime pairing in the Last Word with a rye and lemon combo for his Final Ward, Simó wanted to riff on the Last Word spec himself. He quickly hit a roadblock.

“I was stuck thinking in this framework of single liqueurs,” says Simó. He was hesitant to add another botanically complex liqueur on top of yellow Chartreuse. That’s where the Paper Plane came in. As soon as he tried that drink, he changed his thinking.

“I started reaching into the amari, and that’s when the progress got much quicker,” says Simó. Soon he was slipping his mix of mezcal, Yellow Chartreuse, Aperol, and lime to regulars and its popularity landed it on the Death & Co. menu in the fall of 2011. The drink went on to be a global sensation, gracing cocktail menus from Portland to Paris.

“I get texts a few times a week with pictures of the Naked and Famous on a cocktail menu in Rome, in Seville, in Buenos Aires, and it makes me happy,” Simó says. “It’s my sluttiest recipe ever.”