The substitution of a cocktail onion for an olive or a lemon twist turns a martini into a Gibson. These citrusy orbs are especially wonderful with gin.
Bring juice to a simmer in a small pot, and simmer until reduced by half. Add vinegar, salt, zest, and onions, and gently simmer 10 minutes. Remove from heat. Let cool, then transfer to a glass jar with a tight-fitting lid. Refrigerate onions at least 8 hours before serving.