1. Preheat oven to 350 and grease 9x13 baking pan with nonstick cooking spray. Set aside. 2. Mash sweet potatoes in a large bowl. 3. In a small bowl add butter, sugar, apple juice and cinnamon and mix well. Pour mixture into the large bowl of Sweet Potatoes and mix well. 4. Spread mixtures into prepared pan. Pat mixture flat with the back of a spoon. Top with marshmallows. 5. Bake for 20-25 minutes until marshmallows are puffy and sweet potatoes are heated through.