Wash the sweet potatoes but do not peel them. Bake whole in a baking dish at 350 degrees for an hour.
Cut in half and remove from skin. Mash with fork or potato masher, then mix in all other casserole ingredients.
Bake at 400 degrees for 20 minutes in a 9x13x2 pan. Meanwhile, mix the topping ingredients. Put topping on and bake 10 minutes more.