Boil sweet potatoes 15-20 minutes until tender; drain and mash.
Preheat oven to 350°F. Mix sweet potatoes with butter, sugar, milk, eggs, vanilla, cinnamon, nutmeg, and salt. Taste and adjust the sweetness or spices.
Spread into a greased 9x13-inch white ceramic baking dish.
For pecan topping, mix flour, sugar, butter, pecans, and cinnamon; sprinkle over base. For marshmallow topping, spread marshmallows over the base.
Bake 25-30 min until set; broil marshmallows 1-2 min if desired.
Cool 5-10 min, serve in a baking dish with pecans, cinnamon, turkey, and cider.