Preheat oven to 400 degrees. Peel and chop sweet potatoes into 1/2 inch cubes. Set aside. 

In a large non-stick skillet, bring balsamic vinegar and brown sugar to a boil. Turn down heat to medium-low, continue to simmer until vinegar begins to reduce and thicken. Stir in butter and salt. Heat through.

Add potatoes to pan and toss with sauce. Spread out onto a non-stick baking sheet. Bake for 40 minutes, stirring occasionally, until edges are slightly browned.