Open to wash properly
Remove roots and damaged parts. Split leeks lengthways and separate the leaves under running water: grit can hide between layers. If washing sliced leeks in a bowl, lift them out rather than pouring the sediment back over them.
Drain for the dish
A little moisture matters less in soup. For a gratin or sauté, drain thoroughly before softening. Weigh the prepared amount in the recipe, excluding discarded leaves.
Soften without burning
Moderate heat softens the slices. Stir and watch the base; a little water can help if they stick, but let it evaporate for a gratin. Tougher green parts need fine slicing and may need longer cooking.

