Choose firm onions that feel heavy for their size. Avoid those with green sprouts or soft spots. Keep in a cool, dark and well-ventilated place for up to two weeks. Once cut, onions may be kept in a tiighly sealed glass jar in the refrigerator for 2 to 3 days.
Slice off root and stem emds. Remove papery skin and outer layer. Cut to desired size. Browning an onion slowly over low heat (called caramelizing) brings out a sweet, mild flavor; over medium heat, a stronger tast emerges. If cooked quickly in very hot oil, a more jagged flavor develops. All methods are called "browning an onion", buteach produces a big difference in the taste of the dish.