How to Make It
Preheat the oven to 350°. Butter a 13-by-9-inch baking dish. Put the sweet potatoes in a large pot. Cover with cold water and bring to a boil. Cook over moderate heat until the sweet potatoes are tender, about 15 minutes. Drain well, shaking off the excess water. Transfer the sweet potatoes to a food processor (in batches, if necessary) and puree until smooth.
Scrape the puree into a large bowl. Add half of the butter, 2 teaspoons of salt, 1 teaspoon of the nutmeg, 1/2 cup of the brown sugar and the milk and stir until combined. Stir in the eggs. Pour the mixture into the prepared baking dish and smooth the surface. Cover with foil and bake for 40 minutes.
Meanwhile, spread the pecans on a baking sheet and bake for 5 minutes, until lightly toasted. Transfer the pecans to a work surface and coarsely chop them. In a bowl, toss the pecans with the cornflakes, cinnamon and the remaining melted butter, 1/2 teaspoon of nutmeg and 1 cup of brown sugar. Season with salt.
Remove the foil from the casserole. Spoon small clumps of the topping all over the sweet potatoes. Bake, uncovered, for 40 minutes longer, until the topping is golden and sizzling. Let the casserole stand for 20 minutes before serving.