12 medium leeks, trimmed to about 7 inches, split length-wise to within 1 1/2 inches of the root end
Olive oil for grilling
4 teaspoons Dijon-style mustard
3 tablespoons white-wine vinegar
1/2 cup extra-virgin olive oil
1/3 cup minced assorted fresh basil
Tie the leeks in 4 bundles with kitchen string, and place in a kettle of boiling salted water. Boil them for 6 minutes, or until they are just tender, and drain them in a colander. Refresh the leeks under cold water and discard the strings. Brush the leeks with the oil and grill them on an oiled rack set, 5 minutes on each side, or until they are golden.
Transfer the leeks as they are grilled to a platter and keep warm. In a separate bowl combine all the vinaigrette ingredients and season with salt and pepper. Drizzle the vinaigrette over the leeks.