Ingredient

Leek

A leek is a milder, sweeter, more delicate allium than an onion, and it collapses into something silky in a way an onion never quite does. It also grows with soil packed between its layers, so washing it properly is not optional.

How it differs from an onion

Leeks contain less of the sulphur compounds that make onions sharp and make you cry, and more sugar. Cooked slowly in butter they go sweet, soft and almost creamy, where an onion would still have some bite and a stronger flavour.

That makes them the better choice where you want an allium base to disappear into the background — a delicate soup, a fish dish, a quiche, a cream sauce. Where you want the allium to assert itself, use an onion.

The dark green tops are tougher and more strongly flavoured than the white. They are not waste: they go into stock, or can be sliced very finely and cooked longer than the white parts.

Washing the grit out

Soil gets between the layers as the leek grows, and rinsing the outside does nothing.

1. Trim the root and the coarsest dark green top.
2. Slice the leek in half lengthways, or cut it into rounds first if the recipe wants rounds.
3. Fan the layers under cold running water, or drop the sliced rounds into a large bowl of cold water.
4. Swish them about vigorously and leave them for a minute. The grit sinks.
5. Lift the leeks out of the water with your hands — do not pour the bowl into a colander, which tips the grit straight back over them.
6. Drain well. Wet leeks steam rather than softening in butter.

How to cook them

Sweated in butter

The default. Sliced, covered, on a low heat with a pinch of salt for ten to fifteen minutes until completely soft and sweet.

Braised whole or halved

In stock and butter, gently, until a knife slides through. Then finished under a grill or with breadcrumbs.

Roasted

Halved lengthways, oiled, cut side down at a high heat. The outside chars and the inside goes silky.

In soup

Leek and potato is the obvious one, and it works because the leek supplies sweetness and the potato supplies body.

Raw

Very finely sliced in a salad, though it is sharper raw than cooked.

Not for

Fast, high-heat cooking. Leeks want time and gentleness, and a hot pan makes them stringy and scorched.

Buying and storing

• Look for firm, straight leeks with plenty of white and pale green, and tight, unblemished tops.
• Avoid any that are soft, splitting, or have a woody-looking core showing at the cut end — that is a leek that has started to bolt and it will be tough.
• Smaller and thinner is generally better. Very large leeks can have a tough central core.
• They keep well — a week or more in the fridge, wrapped loosely. Do not seal them tightly; they sweat.
• They freeze acceptably once sliced and cooked, less well raw.

Common questions