Grilled Sweet Potatoes with Lime Cilantro Vinaigrette

2 pounds sweet potatoes (about 4, preferably long)
2 tablespoons fresh lime juice
3/4 teaspoon kosher salt
1/8 teaspoon black pepper
1/4 cup olive oil
2 tablespoons chopped fresh cilantro leaves

Cover potatoes with cold water in a large pot, then bring to a boil. Simmer until slightly resistant in center when pierced with a sharp small knife, 25 to 30 minutes, then transfer to a large bowl of cold water to stop cooking. Drain well. When cool enough to handle, peel potatoes with a sharp small knife and quarter lengthwise.

Prepare grill for cooking.

Whisk together lime juice, salt, and pepper and add oil in a slow stream, whisking. Whisk in cilantro.

When fire is hot (you can hold your hand 5 inches above rack for 1 to 2 seconds), grill potatoes in 2 or 3 batches on lightly oiled grill rack (over coals if using a charcoal grill), uncovered, turning, until grill marks appear and potatoes are just tender, 3 to 6 minutes total.

Serve potatoes warm or at room temperature, drizzled with vinaigrette.

Cooks' notes:
Potatoes can be boiled and peeled 1 day ahead and chilled, covered. Vinaigrette can be made 2 hours ahead and kept at room temperature.

If you aren't able to grill, potatoes can be cooked in a well-seasoned ridged grill pan over moderately high heat, turning, until grill marks appear, 3 to 6 minutes total.

Yield: 6 to 8 servings