I seem to be getting more tech support questions from people who are relatively new to the Mac.
@leebennett I know it sounds crazy, but it works. The onion (or garlic) likes the metal more than your skin.
@leebennett No, not something abrasive. Just rub a stainless steel spoon or chef's knife (or even a sink) under cold running water.
@leebennett Rub with stainless steel and cold water.