When Jayce McConnell of Edmund’s Oast in Charleston, South Carolina, wants to add a little something extra to a cocktail, he often reaches for the Chartreuse—a 130-ingredient liqueur made by French monks since the 1600s, and now widely available in the United States “It imparts balanced sweetness, booziness, and herbal complexity the way no syrup can,” he says. “Why not use it in an herb-driven drink like a julep?”