Boil sweet potatoes about 10 minutes. Remove skin and slice. Preheat oven to 325 degrees. Place sweet potato slices in shallow baking dish. Mix with white and brown sugar, vanilla, nutmeg and flour. Pour mixture over sweet potatoes and fold without breaking the potatoes too bad. Pour in greased baking dish. Cut the butter into slices and dot on top of the potato mixture real well. I'm kinda from the same school as Paula Dean, you can't have enough butter (If you use more than 1.5 it's fine). Bake 35 min. Add the marshmallows over the top and bake for 15-20 min more until browned. Note: If you are using the 2 large cans cooked rather than the fresh sweet potatoes/yams, Follow directions but obviously don't boil. Drain the liquid out of the can. Happy Holidays ;)