In his new book, Modern Classic Cocktails: 60+ Stories and Recipes from the New Golden Age in Drinks (available October 4), Robert Simonson shares the origin story of Erick Castro's Piña Verde. His Piña Colada riff trades the rum for green Chartreuse. "It all began with a little bartender trick, designed to make a good drink better—or, at least, stronger," Simonson writes. When Castro was the Beefeater Gin brand ambassador in the late aughts, he, at first, attempted to make a Piña Colada with gin versus rum. "In time, Castro came to realize that what he liked most about the cocktail was the interplay between the Chartreuse and coconut," Simonson adds. "So he ditched the gin altogether and allowed the overproof French herbal liqueur to step into the starring role."