Leeks are cousins of the onion, but have a harsher flavor when eaten raw and a milder flavor when cooked. Leeks are good sources of vitamin A and C, which aid the immune system. Leeks can be harvested at a variety of sizes, but most often feature a six to 10-inch stem.
The leek has white and green leaf sheaths that wrap around each other to form a stalk. Choose firm, crisp stalks and refrigerate in a plastic bag up to two weeks. Wash thoroughly by soaking in cool water. When cooking with leeks, most recipes call for trimming the uppermost dark leaves to avoid bitter and woody flavors.