It’s a whisper on the tongue. An almost ghostly presence amidst the familiar dry grip of bitters and a smooth herbal warmth that is green chartreuse. Is it…cream? Is it…vanilla? In a drink that is, as Roquette proprietor Erik Hakkinen puts it, “the brownest brown cocktail I’ve ever seen,” this rich, almost buttery tang is the best kind of confusing.

Roquette’s Coco Richards, an off-menu holiday drink special, reveals new dimensions with every sip. By the time the stately block of ice has melted down, what was once spirit-forward and brioche-y is now soft and citrusy. It feels as though I have witnessed some preternatural act of cocktail alchemy. I’m at a loss as to how a drink that could be a manhattan—amber-colored and garnished with a deft twist of orange peel—has the creamy mouthfeel and flavor profile of a chocolate milkshake. A Dick’s chocolate milkshake, according to Hakkinen. The Coco Richards comes upon its dulcet tones thanks to an actual milkshake from the fast food chain, deployed via a process called fat-washing.

This technique has been around for a while, and to Seattle’s seasoned bartenders it can seem as old-fashioned as…an old fashioned. But a new, more sophisticated generation of fat-washed cocktails has quietly come of age on drink lists around the city. And they’re especially prevalent this time of year, when all things hot chocolate- and eggnog-adjacent reign supreme.

There are a few ways to approach fat-washing, and Hakkinen’s take is straightforward, if messy. He puts all the ingredients—in this case, Highland Park cask strength Scotch, Giffard pineapple liqueur, the green chartreuse so ubiquitous in Roquette’s cocktails, allspice bitters—in a six-quart, plastic container. Next he dumps in two Dick’s milkshakes, melted into a glorious slick of chocolate. After a 20-minute soak, the laborious task of straining out the liquid fat with coffee filters ensues. The end product tastes of milk without any of the actual shake.

Jon Christiansen of Ba Bar and Monsoon says that he came across fat-washing amid the bacon frenzy of the 2010s. The suddenly pervasive novelty cocktails sporting buttery and porky undertones failed to impress him, and of fat-washing during its initial 15 minutes of fame, he says, “It was kinda hyped, then had been done.” But the abundance of really good pho broth fat at his disposal, as the beverage director at two Vietnamese restaurants, proved too tempting to ignore.

Christiansen’s approach to fat-washing differs slightly from Hakkinen’s, mostly in how the fat solids are removed once they’ve soaked in the spirit. At Monsoon, they skim solidified fat off chilled broth, melt it down into liquid form, and then stir or shake it to combine with Trail’s End bourbon. Rather than straining this bourbon-pho mashup, he and his team chill it so the fat solids coalesce once more. Then, they can be wicked away from the top. The resulting Old Phởnky Fashioned boasts a silky mouthfeel and savory aromatics.

Phocific Standard Time’s Katharine Frazier also swears by the freezing strategy, producing a pho fat-washed cocktail that Hakkinen opines has an “almost mega pho pickle back thing going on.” Rather than merely a faddish technique used to produce kitschy novelty drinks, Frazier considers fat-washing to be highly versatile, capable of elevating the complexity of any spirit.

The sheer adaptability of the technique is perhaps what saves it from being a passing trend. Hakkinen is determined to perfect a Nutella wash which has thus far proved temperamental. Meanwhile, Christiansen “has shrimp paste percolating on the brain.” The future is fat with promise.