You could do them up as we, here in the U.S. do at Thanksgiving. First, you're calling them "sweet potatoes", but are they that or are they Yams? Sweet potatoes aren't nearly as orange as yams and are not as sweet.
At any rate, boil two or three until barely fork tender, peel, slice in 1/2 inch slices, arrange a layer or two in a baking dish and sprinkle about 1 cup (a double handful) of brown sugar over them. Place them in the oven at about 350 degrees (F) for about 1/2 hour, remove and top with a cup or so of marshmallows and return to the oven just long enough to slightly brown the 'mallows... serve warm...