Butter coffee is a beverage made with brewed coffee and unsalted butter. It was popularized as a morning drink for followers of the keto diet, who will often add manufactured medium-chain triglycerides (MCTs) to it.
It was originally popularized in Western markets by Dave Asprey, a technology CEO who sample yak butter tea in Tibet; Asprey's company produces a branded butter coffee product called "Bulletproof Coffee."