Wash the sweet potatoes well, and cut in half.  Add the sweet potatoes and cinnamon sticks to a large stock pot, cover with water, and boil until fork tender, about 25 minutes. Drain water, discard cinnamon sticks, and remove peel from cooked sweet potatoes.

Heat oven to 350⁰F/176C⁰. Place the sweet potatoes in the bowl of a large electric mixer, and whip briefly to make a puree. Remove the long fibrous strands that accumulate on the beater blade. Stir in the maple syrup. Spread the puree in a large casserole dish.  Top with freshly ground cinnamon and pecan pieces. Cover with foil, and bake until well heated, about 45 minutes.

Remove the casserole from the oven, remove the foil and top with the marshmallows. Turn on the broiler, and briefly toast the marshmallows. You’ll have to stand guard at the oven door, as the marshmallows are delicate and burn quickly. Serve immediately.