In a large bowl, combine mashed sweet potatoes, melted butter, sugar, brown sugar, beaten eggs, milk, cinnamon and nutmeg. Spoon into a greased 1 1/2 quart baking dish. Bake, uncovered, for 20 minutes.
In a small bowl, combine crushed cornflakes, walnuts, brown sugar and cubed butter. Sprinkle over potato mixture.
Bake again for 5 to 10 minutes or until topping is lightly browned.
Watch this video to see how to make this delicious recipe!