Bitters
Credit: Didier Descouens / Wikipedia

Bitters are concentrated infusions of barks, herbs, and roots, and just a few drops will elevate a simple drink into a refined cocktail. Angostura has earned its longevity through quality, but it's not the only choice. There is a bitters renaissance right now with a slew of small-batch artisanal bitters with a wide range of flavors. Try the Hella Bitter, Bittermens Hellfire Habanero Shrub, or Scrappy's Bitter Cardamom