Slender haricots verts are best for this salad. If you can only find regular green beans, slice them thinly. The truffle oil really makes this salad special. Walnut oil or a good olive oil would make a fine substitution.
In a small bowl, whisk the mustard, vinegar, thyme, salt, and pepper. Slowly drizzle in the truffle oil, whisking constantly, to make a creamy, emulsified dressing; set aside.
In a large bowl, toss the blanched beans, mushrooms, shallot, and sliced endive with the vinaigrette. To serve, line a platter with the whole endive leaves and mound the salad over them.
nutrition information (per serving):
Photo: Mark Ferri