Leeks are a member of the onion family with a sweeter and more mellow flavor than yellow or Spanish onions.
If you’ve never cooked with leeks before, I’d recommend substituting it for onion in a favorite recipe. Because leeks grow in sandy soil, you will find grit deep between the leaves. To clean them, pick away any tough outer leaves, slice from the root (without cutting through the root) all the way through the leek lengthwise, creating a V. Submerge in water for 10 minutes. Use your fingers to make sure the water gets between each layer. The green leaves are great to flavor stock, while the white and yellowish parts can be used wherever you would use onion in your recipes. I also love leeks also served as a side dish, steamed then dressed with olive oil and red wine vinegar, and topped with some walnuts.