Ingredients:

  Amount  Measure       Ingredient -- Preparation Method
--------  ------------  --------------------------------
   2                    sweet potatoes -- about 4 pounds
     1/4  cup           balsamic vinegar
   1      tablespoon    sugar
     3/4  teaspoon      butter -- cold
   1 1/2  teaspoons     olive oil

Preparation:

Scrub sweet potatoes well. Place in a large pot and cover with cold water.= Bring water to a boil, reduce heat, and simmer until almost ternder. about= 40 minutes (they should be a little undercooked). Remove from heat and= drain; peel and set aside. (Sweet potatoes can be prepared 1 day in= advance up to this point) Combine balsamic vinegar and sugar in a small= saucepan over high heat. Simmer mixture until it is thick and syrupy, or= reduce by one-half, about 10 minutes. Remove form heat, add butter and= cool. If using grill, heat grill to high. Cut sweet potaotes crosswise into 1/2= inch thick slices. Brush tops of slices with oil and place, brushed side= down, on grill until marked, about 2 minutes. While slices are cooking.= brush the other sides with remaining oil and turn over. Grill until marked,= about 2 minutes more. Brush grilled sweet potatoes on both sides with= vinegar glaze and serve. If using broiler, heat broiler to high. Arrange sweet potatoe slices on a= baking sheet and brush tops with glaze; no oil is necessary. Place baking= sheet under broiler and broil until galze starts to bubble, 3 to 4 minutes.= Remove from oven, turn potatoes over, and brush with glaze. Broil for 3 to= 4 minutes more.