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Leeks are like the Lord Thistelwick Flanders of the onion family. The refined and aloof European cousin who needs to be nudged before his true onion character emerges. But once you start cooking with them, they offer a variety of characteristics that you don't find in regular onions.
First off, texture. When you cook down a regular onion, it becomes very soft, or it completely disintegrates. Leeks, on the other hand, retain a bit of tender bite, acquiring a pleasing texture more similar to that of, say, cooked cabbage. This property makes them fantastic whenever you want to add nice mild onion flavor without the stringiness or pulpiness of regular onions. Cooked very slowly in emulsified butter (often described on menus as "leek fondue"), they are incredible.
Flavorwise, they are far more mild than a regular onion, without the sweetness of a shallot. Slightly grassy and vegetal, they are known as the "soup onion" for a reason—they are great in soups and stews. Their flavor tends to sit back and support other flavors without overwhelming them.
Leeks are also quite versatile. They can be stewed, braised whole, roasted, sautéed, and as any chef from the early '90s can tell you, deep fried into crisp frizzles to add texture to soups and salads (though your soup will end up looking like Don King).
Shopping and Storage
Look for leeks with tight, bright green tops that aren't wilting at all. The white bases should be bright white—yellowing is a sign of age. At the supermarket, most leeks these days are pristine with no dirt at all, but if you do find muddy leeks, it's ok, and should be expected, as leeks grow pretty deep in sandy soil. Just be sure to carefully wash away all grit and sand before cooking with them (I go over this in the video).
Since they don't have the robust dried exterior of a standard onion, the shelf like of leeks is far shorter. Leeks can be stored in a plastic vegetable bag in the crisper drawer for about 2 weeks or so, though 1 week is more normal. Generally, I buy them as I need them instead of treating them as a pantry staple.
Only the tender white and light green bottoms are actually eaten, but the fibrous green upper parts still have plenty of flavor and can be added to the pot next time you make stock.
And finally, I had a bad cold this week (which explains the soup-friendly leek video), so please welcome Robyn Lee in the premier of her voiceover career. One man's hoarse throat is another woman's career-launcher.
When do you guys pick leeks over regular onions?