As vegetables go, few have as much flavor potential as leeks. However, they are also one of the dirtiest vegetables around. To clean a leek meticulously, first cut off the coarse stringy roots. Because most of the long dark leaves are tough and woody, cut off all but 1 1/2 inches of that part. (If desired, after a thorough washing, use these in stock.) Using a sharp 8-inch chef’s knife, cut down the entire shaft of the leek. If planning to braise them whole, don’t cut all the way through the bottom (outside) layer. The dirtiest part of the leek is where it changes from light green to a darker shade.
Open the leek, like a book (keeping the layers intact) and, starting at the green end, held horizontally to the side (or dark green pointed down), rinse the leek thoroughly, under cool water. Look through all the white and green layers, checking for dirt and, after wiping the leek dry, slice it or leave it whole, depending on your particular recipe.