CILANTRO SAUCE:

1 c. low-fat plain yogurt
1/2 c. sour cream
1 fresh jalapeno or other hot chili pepper, cored, seeded, and very finely chopped
1/4 c. chopped fresh cilantro
2 tbsp. grated raw onion
3 tbsp. bottled salsa (hot or mild)

In a bowl, stir together the yogurt and sour cream. When the mixture is smooth, add the jalapeno or hot pepper, cilantro, onion, and salsa. Stir again, and when the sauce is well blended, cover it tightly with plastic wrap and refrigerate for at least 15 minutes (you can store this sauce for up to 2 days).

SWEET POTATOES:

6 lg. sweet potatoes, rinsed, with skins intact
1/4 c. olive oil
Salt and freshly ground black pepper, to taste

Light the grill.

Cut the sweet potatoes lengthwise into 8 spears each (you will have 4 dozen all together). Set them, skin down, on a rimmed baking sheet. Brush the cut sides with oil.

When the coals turn gray, place the spears on the grill, cut sides down. Cook the potatoes for about 8 minutes, turning them often, until they are charred in spots and cooked through (test them with the tip of a knife to make sure they're soft).

Arrange the potatoes on a large platter and serve with the cilantro dipping sauce.