The choice of spirits gives a drink its character and the mixers its balance, but the addition of aromatic bitters is what lends many classic cocktails their depth. These days, mixologists often make their own bitters by infusing Everclear or overproof whiskey with spices, botanicals, and seasonal fruit. At Proof & Provision, the cocktail bar tucked in the basement of Atlanta’s historic Georgian Terrace Hotel, barkeep Nate Shuman conjures a smoky sense of place with his distinctive barbecue bitters. Shuman adds a few drops to a wickedly alluring rye-and-mescal-based concoction that he calls the Plaza en Fuego, but you can also use this secret-sauce elixir in a Manhattan or anywhere brown spirits reign. Bonus: The added hit of smokiness and spice works great in a Bloody Mary.