There are fresh onions with long green stems (”spring” onions); and scallions (often called green onions) are obviously fresh as well. But most onions are dried before sale and may be white, yellow, or red; pungent, mild, or sweet-the variety is astonishing.

The onion is the bulb of a plant related to the lily, so the fact that it and other alliums (even garlic) are quite attractive in bloom is not surprising. Dry onions are essentially interchangeable, though red and white onions are milder, and I’ve come to believe that white onions are really the best for all-purpose use, though it’s not a position I could defend readily.
Sweet onions, including Maui, Vidalia, and Walla Walla, have a less pungent flavor, are juicy and sweet, and usually have a flatter spherical shape than other dry onions. They are the best onions for eating raw, though they’re fine for cooking too.
On the smaller side are pearl (or boiling) and cipollini onions. Pearl onions are about the diameter of a quarter and are ideal for boiling, braising, and stewing; their small size allows them to cook through whole. Cipolline can be used the same way as pearl onions, and their completely flattened shape adds an interesting look to any dish.
Scallions and small bulb onions with green stems attached are “fresh” or “spring” onions; they are generally milder in flavor and softer in texture. Scallions in particular are often used raw as a flavorful oniony garnish for salads, soups, dips, and other dishes. Their small size makes them extremely valuable as a garnish.
Buying and storing: Fresh onions should have vibrant green, fresh-looking, crisp stems and unblemished white bulbs. Dry onions should be firm and covered tightly in at least one layer of shiny, tan to yellow or deep red skin (the outer skin of white onions is more papery).
A strong onion aroma is an indication of damaged or rotting onions and should be avoided; also avoid sprouting onions. Store fresh onions in the refrigerator and dry onions in a cool, dark, airy spot or in the refrigerator, for weeks.
Preparing: If you have a lot of onions to peel, drop them into boiling water for 30 seconds to 1 minute, then rinse in cold water. Slice off the stem end and the skins will slip off easily. For just a couple of onions, cut a thin slice off the stem end, then make a small shallow cut, just through the skin and top layer of flesh; peel off both together. Then slice or chop as needed.
If you’re peeling and chopping a lot of onions, you might consider wearing goggles; but a properly sharpened knife also mitigates the amount of tear-inducing chemical released into the air. (This substance, called lachrymator, combines with the moisture in your eyes to form a weak solution of sulfuric acid. No wonder it burns!)
Leave the root end on onions you will cook whole; they’ll stay together better.

Best cooking methods: Caramelizing, roasting, and grilling.
When is it done? When very tender but not quite falling apart.
Other vegetables to substitute: Shallots or leeks.
Leeks
The leek looks like an enormous scallion, which it kind of is-like scallions, it’s a member of the allium genus, along with onions and garlic. Mild and sweet, silky when cooked, leeks have only one downside: their cost.
If you’re paying by the pound, make sure there is plenty of white on the stalk; you’ll trim off most of the green.
Buying and storing: Generally, the smaller the leek, the more tender; but big, plump leeks are wonderful too. Avoid those that are slimy, dried out, browning, or mostly green. Store loosely wrapped in plastic in the refrigerator; they will keep for weeks.
Preparing: Wash well; leeks usually contain sand between layers. The traditional process: Trim off the root end and any hard green leaves. Make a long vertical slit through the center of the leek, starting about 1 inch from the root end and cutting all the way to the green end (leaving the root end intact helps keep the leek from falling into pieces when you wash it.)
Wash well, being sure to get the sand out from between the layers. The easy way, which works only if you don’t want the leeks whole: Trim, chop, and wash in a salad spinner, as you would greens.
Best cooking methods: Sautéing, braising, roasting, and grilling.
When is it done? When soft-almost melting.
Other vegetables to substitute: Onions, shallots, or scallions.

Shallots
A member of the allium family (which contains not only onions and garlic but also lilies), shallots have a mild but complex flavor, making them the queen of the category. They come in individual cloves, not unlike garlic but bigger, with the flesh and flavor of a mild onion. They have a tan, papery dried outer skin that tightly covers each clove, and the inside flesh is semitranslucent white with a tinge of purple or green.
Buying and storing: Shallots should be firm and have a pretty, shiny tan outer skin. Their shape is distinctive; usually two cloves held together at the root end to make an oval shape with tapered ends. Don’t be fooled by small, round, tan-skinned onions often labeled as shallots. Store in a cool, dry place or in the refrigerator for weeks.
Preparing: Break the cloves apart and remove the dry skins; trim the stem end and slice or chop as you would an onion.
Best cooking methods: Sautéing and roasting.
When is it done? When tender and translucent.
Other vegetables to substitute: Scallions are closest; onions (especially red or white) and leeks are also good.


























