1. Cook potatoes in boiling water to cover for 20 minutes or until tender. 2. Let the potatoes cool to touch; peel and mash potatoes. 3. Stir in cranberry sauce and cinnamon. 4. Transfer mixture to a lightly greased 2-quart casserole. 5. In a mixing bowl, combine flour, sugar, and oats; cut in butter until mixture looks like coarse crumbs. 6. Spoon crumbs over sweet potato mixture. 7. Bake in a 375° oven for 20 minutes. 8. Top with marshmallows and bake until golden brown.
