To clean leeks, trim off the root end and then the dark green tops. Sometimes, in the middle of the leek, you can find some inner light green layers buried within dark green outer layers, and it’s worth cutting off the dark green leaves in the middle and peeling them away to get the light green core.
Wash the cut or trimmed leeks extremely well under cold water just before using. You can halve them lengthwise. Or, if you are slicing or chopping them for a recipe, you can do that before rinsing them to make it easier to remove the dirt.
Again, just use the white and light green parts. You can slice them crosswise into disks, that will separate as you cook them. Or slice the leeks lengthwise and then slice them into half moons (which will also fall apart). You can also chop them; one easy way to do that is to slice the leeks lengthwise into strips and then cut them crosswise.
Notes
Wash the cut or trimmed leeks extremely well under cold water just before using. You can halve them lengthwise. Or, if you are slicing or chopping them for a recipe, you can do that before rinsing them to make it easier to remove the dirt.