In a large bowl, combine the dry ingredients. Combine egg, buttermilk, and oil; mix well. Stir into dry ingredients just until moistened. Fold in chocolate chips and 1 cup marshmallows. Fill greased jumbo muffin cups 3/4 full. Sprinkle with remaining marshmallows. Bake at 375? for 18-20 mins or until a toothpick comes out clean. Cool for 5 mins before removing from pan to a wire rack. Serve warm. These freeze well.