The Old-Fashioned, Manhattan, sidecar and other 19th- and 20th-century staples are making a comeback on cocktail lists. Many of these classics rely on brown spirits—a category that is seeing growth, with whiskey and bourbon up 6.6% year over year, according to Technomic’s MenuMonitor. Some chains are giving these retro drinks a more contemporary twist, barrel-aging the spirits to deepen the flavor and adding housemade or artisanal bitters to elevate the recipes.