Leeks are like onions, only milder and more buttery when cooked. Leeks are generally sold with their greens attached, but unlike scallions, leek greens aren’t intended for consumption. As such, the first step a leek must undergo in your kitchen is trimming. Remove the tough greens and trim the roots, so that you are left with the tender white length of the leek. Also of note here is that leeks are famously prone to hiding dirt within their layers and therefore must be cleaned carefully before use.
The easiest way to clean them is to slice them in thin cross sections and then plop the slices into a bowl of water, but it’s also possible to keep them in their original form, as this recipe calls for, and clean them by manually spreading their layers. If you want more guidance on how to trim and clean a leek, check out the foreword to this recipe—it goes much more in depth and has photos to guide you!