This sweet potato casserole is always going to be amazingly nutty and crunchy, but adding cornflakes cereal to the pecan-brown sugar topping gives the casserole extra crispiness. Each topping tastes beautifully toasty, and comes together in a medley of flavors all rolled into a single bite. The Cornflake, Pecan, and Marshmallow-Topped Sweet Potato Casserole is a rich and filling dish, sweet and savory at the same time. Set this down on the sideboard for a buffet-style Thanksgiving meal and your friends and family will be piling their plates high. They’ll also marvel at how beautiful it looks with its rows of cornflakes, pecans, and marshmallows spread diagonally across the top.