Using a knife, poke holes in sweet potatoes.
Place potatoes on a large baking sheet lined with foil, bake at 350 for 1 hour.
2. Let potatoes cool completely. After cooled, peel and slice into 1 ½ inch rounds.
In an ungreased 9x13 baking dish put 1 layer of sweet potatoes, 1 cup of brown sugar and 1/3 of the bag of marshmallows. Put another layer of sweet potatoes the other 1 cup of sugar Cover and Bake at 325 for 3 hours, or until juice is the consistency of thick syrup, basting occasionally. Add remaining marshmallows and put under broiler until lightly browned.