Put the potatoes in a large pot, cover with cold water, add 1 tablespoon kosher salt, bring to a boil and cook until a paring knife inserted into the center of the potatoes meets with some resistance. (Do not cook through.) Drain and let cool slightly.
Mix together the butter, molasses, cilantro, orange zest and nutmeg and season with salt and pepper. Cover and refrigerate until ready to use
Heat a charcoal or gas grill to medium high for indirect grilling.
Cut off a thin slice of each potato lengthwise to create an even base for the potato to rest on. Slice off the ends of each potato. Rest each potato between two chopsticks or wooden spoons placed lengthwise along the potato (to act as a stop for the knife) and carefully cut vertical slits about every 1/8 inch.
Brush the potatoes with the canola oil and season with salt and pepper. Place the potatoes on the cooler side of the grill, cover and cook until lightly golden and cooked through, 12 to 15 minutes.
Place the potatoes on a platter and immediately smear the tops with the butter mixture, making sure it melts into the cuts. Heat the rum in a small saucepan, flambe and pour over the potatoes. Serve immediately.
Use extreme caution when igniting alcohol. Remove the pan from the heat source before adding the alcohol. Pour the alcohol into the pan and carefully ignite with a match or click lighter. Return the pan to the heat and gently swirl to reduce the flames.