Leek are long and cylindrical vegetable with dark green leaves and white roots. Select small to medium size which are bright with unblemished leaves. How to use :- Trim the leeks, discarding the roots and tough green tops. Slit the leeks lengthwise in half and wash thoroughly under cold running water. Place each leek half, cut-side down on the chopping board. Cut across into about 1/4 inch slices.