Preheat oven to 375ºF. Soak raisins in sherry until soft, about 30 minutes. Drain raisins and transfer to a large bowl, discarding sherry. Meanwhile, place sweet potatoes in a roasting pan and bake until tender, about 40 minutes. Allow potatoes to cool, the peel, puree with a food processor or food mill, and add to raisins. Add brown sugar, butter, orange juice, orange zest, and pumpkin spice and mix well. Fold in pecans and pineapple and transfer to an 8 inch baking dish. Bake casserole for 20 minutes, then cover with marshmallows and bake until marshmallows are golden, about 5 minutes more.