Bring vinegar, sugar, cumin, and salt to a boil in a 2-quart non-reactive heavy saucepan, then reduce heat and simmer, stirring occasionally, 5 minutes. Add onions and simmer, stirring occasionally, 2 minutes, then transfer to a bowl and cool. Stir in cilantro. Pickled onions can be made 1 week ahead and chilled, covered.
Copyright July 2003, Gourmet magazine. Printed with permission.
Chef Thomas Keller, author of Ad Hoc at Home, explains how to season food with salt and vinegar, and why you should temper your food.