2½ pounds fingerling or small new potatoes, halved (quartered if large)
Coarse salt and freshly ground pepper
¼ cup olive oil
3 tablespoons Dijon mustard
2 tablespoons sherry (or white wine or cider) vinegar
1 small shallot, minced (2 tablespoons)
3 tablespoons chopped fresh parsley
1 teaspoon chopped fresh thyme
¼ of a small red onion, sliced
Place potatoes in a large pot and cover with cold water; season generously with salt. Bring to a boil, then reduce heat to a simmer and cook until potatoes are tender, about 15 minutes. Run under cold water to cool slightly, then drain.
While potatoes are cooking, whisk together olive oil, Dijon, sherry vinegar, shallot, parsley and thyme in a large bowl. Add salt and pepper to taste. Add potatoes and onion and toss to coat. Serve at room temperature.