Trim leeks to about 5 inches and trim root ends, leaving them intact. Cut each leek in half lengthwise and wash well, discarding any tough outer leaves.
In a skillet just large enough to hold them in one layer arrange leek halves, cut sides down, and add enough water to reach halfway up sides of leeks. Simmer leeks, covered, until tender, 5 to 10 minutes, and immediately plunge into a bowl of ice and cold water.
In a small bowl whisk together vinegar, shallot, mustard, and salt and pepper to taste and add oil in a stream, whisking. Whisk vinaigrette until emulsified and whisk in capers and parsley.
Transfer leeks to paper towels. Pat and gently squeeze leeks until dry and divide between 2 plates. Spoon vinaigrette over each serving.
Nancy and Tim Bass - Sunburst Tomato