Wash sweet potatoes. Place a sheet of tinfoil into a 9 x 9 baking pan. Leave peel on potatoes and place in pan.
Bake in a 350 degree oven for 1 1/2 hours to 2 hours depending on size or util potatoes stick tender with a knife.
Remove from oven and slit each potato in half. (Peeling can be left on or removed.) Pour melted butter on each half. Combine sugar and cinnamon and sprinkle on top.