Cook sweet potatoes in boiling water 20 to 25 minutes or until tender.
Drain and cool.
Peel potatoes and mash.
Combine mashed sweet potatoes, frosting, vanilla, and cinnamon; mix well.
Spoon into a greased 12- x 8- x 2-inch baking dish.
Bake, uncovered, at 350Â° for 18 minutes.
Sprinkle with marshmallows; continue baking 5 minutes or until thoroughly heated