Not a souffle in the true sense of the word, this recipe can be made ahead and frozen. It reheats beautifully.
Up to 1 week ahead: Preheat oven to 350 degrees. Place sweet potatoes in a large pot with salted water to cover. Bring to boil over high heat. Reduce heat to medium and cook potatoes for 15 minutes or until tender. Remove from heat and drain. Place warm sweet potatoes and butter in a large bowl and whip with an electric mixer. Add brown sugar, raisins, nutmeg, evaporated milk, salt, egg, lemon rind, lemon juice, and chopped pecans. Mix well. Coat a 10-inch round or 7x11-inch baking pan with cooking spray. Transfer sweet potato mixture to baking pan and bake 30 minutes. Cool, cover tightly with plastic wrap, then aluminum foil, and freeze.
1 day ahead: Remove souffle from freezer and defrost at room temperature. When completely defrosted, place souffle in refrigerator. Place shredded coconut in a small, nonstick skillet over medium heat and toss until toasted. Remove from heat, cool, and place in a small zip-top bag. Refrigerate.
Thanksgiving Day: Bring souffle and toasted coconut to room temperature. Press miniature marshmallows into sweet potato mixture in an even layer. Microwave on high for 10 minutes or until marshmallows are melted and sweet potatoes are heated through (you can also do this by reheating in a conventional oven for 20 minutes at 350 degrees). Remove from oven and dust with toasted coconut. Cover with aluminum foil. Place souffle in a heat-saving bag or place in a warm oven (300 degrees) or on a warming tray until serving.