Preheat oven to 350°F. Place 6 of the marshmallows, butter, cinnamon and salt in medium saucepan. Cook on low heat until marshmallows are completely melted and mixture is well blended, stirring frequently.
Place in large bowl of electric mixer. Add sweet potatoes; beat with electric mixer on medium speed until well blended. Spoon into lightly greased 1-1/2-quart baking dish; top with remaining marshmallows.
Bake 15 to 20 minutes or until sweet potato mixture is heated through and marshmallows are lightly browned.