Tie the leeks in 4 bundles with kitchen string, 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. Cut the leeks apart at the root ends and drain them on paper towels. (The leeks may be prepared up to this point 1 day in advance and kept covered and chilled). Brush the leeks with the oil and grill them in batches in a heated oiled ridged grill them in batches in a heated oiled ridged grill pan over moderate heat or on an oiled rack set 4 to 5 inches over glowing coals for 3 to 4 minutes on each side, or until they are golden. Transfer the leeks as they are golden. Transfer the leeks as they are grilled to a platter and keep them warm, covered. (The leeks may be prepared up to the is point 1 day in advance and kept covered and chilled. Reheat the leeks on a baking sheet in a preheated 350°F. oven for 10 minutes, or until they are heated through.) Make the vinaigrette: In a bowl whisk together the mustard, the vinegar, and salt and black pepper to taste, add the oil in a stream, whisking, and whisk the dressing until it is emulsified. Whisk in the herbs, the bell pepper, and the olives. Divide the leeks among 8 plates and spoon some of the vinaigrette over each serving. Serves 8 as a first course. Gourmet September 1990