This is a delicious healthy grilled side or main dish. In Korea, this is commonly served by street vendors, especially during the bitter winter. I enjoy it just as much during the summer. In Korea they dip the sweet potato into the sauce. I typically just split the sweet potato like a regular baked potato, and spoon the sauce over it. The tangy sauce really complements the sweetness of the potato. Something healthy to try and enjoy this grilling season!
Scrub the potato skins and blot dry with paper towels.
When ready to cook, oil the grill grate. Place the sweet potatoes on the hot grate and grill, turning often with tongs, until very well browned and squeezably soft, 30 to 50 minutes.
Meanwhile, prepare the sauce. Combine the soy sauce, sake, sugar, scallions, garlic, and sesame seeds in a small bowl and whisk until blended and the sugar is dissolved. Spoon the sauce into 4 small bowls or ramekins.
Serve the sweet potatoes with bowls of sauce. To eat out of hand, simply dip the potatoes in the sauce and eat away. To serve as a side dish, cut open the potatoes and spoon the sauce over them.