- 2 1/2 lb medium yellow-fleshed potatoes such as Yukon Gold
- 1 tablespoon whole-grain or coarse-grained mustard
- 1 tablespoon white-wine vinegar
- 2 teaspoons finely chopped drained bottled capers
- 1/2 teaspoon salt
- 1/2 teaspoon black pepper
- 3 tablespoons finely chopped shallot (1 large)
- 1/2 cup extra-virgin olive oil
- 1/3 cup chopped fresh flat-leaf parsley
- Peel and quarter potatoes, then cover with salted cold water by 2 inches in a 5-quart pot and simmer, covered, until just tender, 20 to 25 minutes.
- While potatoes are cooking, whisk together mustard, vinegar, capers, salt, pepper, and shallot. Add oil in a slow stream, whisking until emulsified.
- Drain potatoes in a colander and cool slightly. Break up warm potatoes into smaller chunks with a spoon and stir in vinaigrette and parsley. Serve potatoes warm.