Haricots Verts with Shallot Dressing

1 1/2 lb. haricots verts (thin French green beans), trimmed
3 tablespoons extra-virgin olive oil
2 teaspoons Dijon mustard
2 teaspoons white-wine vinegar
1 shallot, minced

Steam beans until just tender, 3 to 8 minutes. While beans are steaming, whisk together remaining ingredients and salt and pepper to taste. Toss beans with dressing and season with salt and pepper.

Active time: 15 min. Start to finish: 15 min.