Loving the flavor and look of Hasselback potatoes, I knew it wouldn't be long until I found myself grilling them again, only this time with sweet potatoes.
In a small bowl, mix together garlic, rosemary, and 1 teaspoon of olive oil. Set aside.
Cut off a thin slice of each potato lengthwise to create a even base for potato to rest on. Slice off ends of each potato. Rest potato between two chopsticks or wooden spoons to act as a stop for the knife and carefully cut vertical slits in each potato about every 1/8-inch.
Rinse potato under running water, fanning out to rinse inside of cut slits. Place potatoes on a plate and microwave at high for 4 minutes. Flip potatoes over and microwave again for an additional 4 minutes.
Light one chimney full of charcoal. When all the charcoal is lit and covered with gray ash, pour out and arrange the coals on one side of the charcoal grate. Set cooking grate in place, cover gill and allow to preheat for 5 minutes. Clean and oil the grilling grate. Brush potatoes with remaining olive oil and season with salt and pepper to taste. Place potatoes on cool side of grill, cover, and cook for 15 minutes.
Spread garlic and rosemary mixture over top of potatoes, cover, and continue to cook until soft in the center and crisp around the edges, 15-20 minutes more. Remove from grill, let cool for 5 minutes, then serve immediately while still warm.