Leeks make a soft, sweet base when you wash between the layers

The washing is part of the recipe

Leeks grow with soil tucked between their layers, so cutting and rinsing them is not optional. Trim the roots and the dark green leaves, split the stem lengthwise, then fan the layers under cold running water. For rings, slice first and wash the pieces in a bowl, lifting them out of the water so the grit stays at the bottom. Dry them well before they meet the pan.

The white and pale green parts are tender enough for almost any dish. The dark leaves are firmer but full of flavour, and I keep them for stock with herb stems and vegetable trimmings. If a leek has a thick outer layer, remove it after washing rather than throwing away half the vegetable before you know what is usable.

Build sweetness slowly

Leeks reward gentle heat. Slice them into half moons, add them to oil or butter with salt and cook until they collapse. A covered pan speeds the softening, but uncover it near the end so excess water can leave. I stir often because the thin edges catch before the middle turns tender. A splash of water is useful if the pan looks dry, but it should not become a leek soup unless that is the plan.

Softened leeks are good in soups, gratins, savoury tarts, mashed potatoes and fillings. They can also be roasted in thick sections. Keep the pieces large enough to hold together, coat them with oil and turn them once. The outside colours while the centre becomes creamy. Finish with lemon or a sharp cheese to balance their natural sweetness.

How to avoid a watery dish

Leeks contain a lot of water, which is helpful for soup and less helpful in pastry or a crisp potato cake. Cook sliced leeks until the pan is nearly dry before adding them to a filling. Let them cool, then squeeze or drain if the mixture still looks wet. This small pause protects the pastry and keeps the flavour concentrated.

For a soup, use the green leaves to make stock and the pale stem for the finished bowl. For a braise, let the leeks sit in a single layer with enough liquid to come halfway up their sides. They should be tender without floating. I add delicate herbs near the end so the leek stays the centre of the dish.

Choosing between alliums

The leeks vs onions guide is useful when a recipe gives you a choice. Use yellow onions for stronger browning and a firmer base, or spring onions when freshness matters more than long cooking. Leeks are the better pick when you want the allium to become soft, sweet and almost creamy.