Gauging the Green

• For most cooking applications, including the majority of sauces, use the white part of the stalk and an inch or two of the light green at the top of the white section. The lighter the green, the more tender the leek. If you have any doubts about whether the green section will work in your sauce, try to bend it. If it doesn't have any give, it is unsuitable for your sauce.

Ditching the Dark

• In a few cases, your recipe will instruct you to use only the white of the leek. In this case, set aside even the tender light green section for another use. This specification has more to do with visual appeal than flavor or texture. When white leek stalks are pureed with cream and white cheese, they create a strikingly visual contrast with dark or bright foods, such as spinach pasta or cooked greens, or act as a foil for the seasonings and herbs sprinkled atop the sauce.

Lopping the Leeks

• To get leeks ready for sauces, start by chopping off the woody bottom of the leek stalk and the darker top section. Unless you are using only the white section, slice into the stalk where the light green band is starting to turn slightly darker. Some people enjoy even the darker green stalk sections, so there is no hard and fast rule about how much green to leave on. Slice the stalk in half lengthwise, then cut the halved stalks crosswise, into half-moon shapes. They are now ready to be cleaned by swishing in a bowl of water and drained.

Turning out the Toppings

• Start a basic leek sauce by sauteing cleaned, chopped leek sections in olive oil or butter until softened. This step takes about 10 minutes. For a lighter sauce, boil the sauteed leeks with chicken broth and lemon juice, cool the ingredients, then puree them in a food processor or with a stick blender. The process for making a richer sauce is much the same, except you might simmer the softened leeks with wine and cream before pureeing, or leave the chopped leeks intact in a wine-cream reduction.