Heat the oven to 400º. Scrub the sweet potatoes and cut them lengthwise into quarters or halves. Place in a baking dish roomy enough to hold them in a single layer.
Combine the rest of the ingredients, except for the sesame seeds, to make a sauce. Brush it over the sweet potatoes, then cover the dish tightly with foil. Bake until nearly tender, 50 minutes to an hour. Remove the foil, baste the sweet potatoes with their juices, and return to the oven until the liquid has reduced to a glaze and the potatoes are fully tender.
Sprinkle with sesame seeds and serve.