1.Heat oven to 350°F. Spray 12×8-inch (2-quart) glass baking dish with nonstick cooking spray.
2.Place sweet potatoes in sprayed baking dish. Pour butter over potatoes. Sprinkle with brown sugar and salt. Top with marshmallows.
3.Bake at 350°F. for 25 to 30 minutes or until potatoes are thoroughly heated and marshmallows are lightly browned.