Preheat oven to 400 degrees. Scrub sweet potatoes; pierce several times with a fork. Place on a foil-lined large baking pan; bake 1 hour or until tender. Remove from oven. Reduce oven to 350 degrees.
When sweet potatoes are cool enough to handle, remove and discard peel. Mash potatoes in a large bowl (should have about 6 cups mashed). Stir in eggnog, raisins, sugar and salt. Transfer to a greased 11x7 in. baking dish.
For the crumble topping, in a small bowl, mix flour, rolled oats, brown sugar, pecans and spices; stir in butter. Sprinkle over sweet potatoes. Bake uncovered, 30-35 minutes or until heated throughout and topping is lightly browned. (Optional) Squeeze desired sour cream topping as garnish.