Place the whole potatoes in a large pot of cold water. Add 2 tablespoons salt, then bring to a gentle boil. Let boil until the potatoes are tender, but still quite firm, about 10 to 15 minutes. You should be able to pierce them with a fork somewhat easily, but the potatoes should still be too firm too eat. Drain and let cool slightly. Heat the grill to medium (about 400 degrees F).
Slice each potato in half lengthwise, then slice each half into 4 to 6 wedges, depending on the size. Each wedge should be about 1/3 inch thick. As you slice the potatoes, peel off their skins (they should come off easily). Place the wedges in a bowl, then drizzle with olive oil. Sprinkle with brown sugar, chipotle chile pepper, and the remaining 1 teaspoon salt. Toss to coat.
Grill the sweet potato fries on each side until they're lightly golden brown, have some grill marks (depending upon your preference) and are tender, about 6 minutes total. Remove to a serving platter. Enjoy hot, sprinkled with cilantro as desired.