Stroll into any bar from San Francisco to New York City, and you're bound to find more than a few folks tossing back shots of a curious, caramel-hued liqueur. A waft of the stuff brings mentholated, herbaceous notes, an earthy mix of woodsy cologne, tea-tree oil and unsweetened cough medicine. "Hmm," you might say to yourself.

"It's too dark to be whiskey, not opaque enough for rum, and nobody's ordered a sweet vermouth since Andie MacDowell in Groundhog Day . . . so what the heck is this stuff?" It's fernet, a 19th-century Italian liqueur that's finally washing up on American shores.