In a large bowl, combine the flour, sugar, baking powder, salt, cinnamon and nutmeg. In a small bowl, combine the egg, milk, sweet potatoes and butter; stir into dry ingredients just until moistened. Fold in cranberries. , Fill 12 greased or paper-lined muffin cups half full. Sprinkle with cinnamon-sugar. Bake at 375° for 18-22 minutes or until a toothpick inserted in muffins comes out clean. Cool 10 minutes before removing from pan to a wire rack. Serve warm.