A member of the onion family, scallions have a white base that's an immature bulb and tall, stalk-like green leaves; both parts are used in cooking. Scallions' dark-green ends have a delicate sharpness reminiscent of chives and a light, crisp texture, but they wilt and discolor when cooked too long, so are often added to a dish just before serving. The white parts have an oniony punch, and because their texture is more substantial, they withstand longer cooking times.
5 scallions = about 1/3 cup sliced (white and light green)
You can often substitute chives in recipes calling for chopped scallion greens; substitute onion or shallot for recipes calling for chopped scallion bulbs.
Choose scallions with full white bulbs and firm green tops. Avoid scallions with soggy or browned green parts—they're past their prime.
Remove a couple of inches from the green tops, which often have a scraggly texture. Rinse scallions under cold running water and pull off any bruised or slimy green leaves. Cut off and discard the root end, or trim it if using whole scallions.
Wrap whole, trimmed scallions in a paper towel and put them in a zip-top bag in the refrigerator. They will keep for up to a week.