This, along with my Roasted Chicken with Potatoes and Vegetables, is my wife's favorite dish, and it should go without saying that these two frequently appear side by side. As far as vegetable sides go, few can match the fervent following enjoyed by leeks vinaigrette.
The proportions of the dressing here are fairly loose — it's really whatever your palate prefers. Some people love the bracing punch of the mustard and choose to bump it up. Others love the sweet, mellow taste of the leeks and barely dress the vegetable. Leeks are particularly fantastic in early spring, when they first start appearing at greenmarkets. Having rested for a full winter in the cold ground, they are mellow, sweet, and truly at their best.
- Make a lengthwise cut in each leek, cutting through the green portion partway through into the white portion. Put the leeks in a large bowl of cold water and swish them vigorously to dislodge any sand or dirt. Let sit in the water for 5 to 10 minutes; the dirt will sink to the bottom. Remove the leeks carefully, leaving the grit in the bowl. Repeat two more times—leeks can get very sandy and gritty, and you want to be absolutely sure that you've cleaned them well.
- Fill a medium sauce-pot with water and add enough salt so the water tastes like seawater. Bring to a boil over high heat. Add the leeks to the boiling water and reduce the heat, if necessary, to maintain a brisk simmer. Cook until the leeks are quite tender when pierced, 8 to 10 minutes. Using a spider, gently lift the leeks out of the water, drain, and set aside to cool to room temperature. (I recommend using a spider rather than pouring the leeks and their cooking water into a colander to drain because on the off chance that any sand is left in the leeks after washing, lifting them out of the boiling water ensures that no grit will come in contact with your teeth.) Carefully blot off any excess moisture.
- While the leeks cook, in a medium bowl, combine the vinegar and mustard and stir together. Season to taste with salt and pepper and let sit for 1 to 2 minutes—the acid will dissolve the salt. Whisk in the olive oil to make a thick vinaigrette.
- While the leeks are still warm, toss them with a few spoonfuls of the vinaigrette—the warm leeks will "fuse" with the vinaigrette better than room temperature leeks will. Garnish with tarragon and hard-cooked egg, if desired. Serve immediately or at room temperature.
TIP: For a slight enhancement of the dish, try adding a bit of finely chopped fresh tarragon at the end. It lends a delicate licorice note to the leeks.
NOTE: If you're serving Leeks Vinaigrette as a brunch or lunch dish, the hard-cooked egg is a nice touch. However, if this is a side dish to a roasted chicken, you may chooseto skip the egg.