How to Make It
Prepare filling: Preheat oven to 400°. Bake sweet potatoes on a baking sheet 1 hour or until tender. Reduce oven temperature to 350°. Let potatoes stand until cool to touch (about 20 minutes); peel and mash with a potato masher.
Beat mashed sweet potatoes, 2 Tbsp. softened butter, and next 5 ingredients at medium speed with an electric mixer until smooth. Spoon mixture into an 11- x 7-inch baking dish coated with cooking spray.
Prepare topping: Stir together crushed cornflakes cereal and next 3 ingredients. Sprinkle over sweet potato mixture in diagonal rows 2 inches apart.
Bake at 350° for 30 minutes. Remove from oven; let stand 10 minutes. Sprinkle miniature marshmallows in alternate rows between cornflake mixture, and bake 10 more minutes.