The Bitter Truth is a German company that offers a range of cocktail bitters, but its celery flavor is the superstar. It makes drinks sing with complex, vegetal depth; in food, too, it brings out the best in other ingredients. When making rhubarb chutney, I poach the rhubarb in honey and add ginger, lime zest, and a few drops of celery bitters. The bitters make you say, "What's that last element I can't quite place?" —Ken Oringer, Clio, Boston