How to Make It
Preheat oven to 350°F. Place potatoes on an aluminum foil-lined baking sheet. Bake in preheated oven until very tender when pierced with a knife, about 1 1⁄2 hours. Cool 30 minutes. Peel and discard potato skins.
Stir together potatoes, shallot, milk, eggs, sage, nutmeg, 1/2 cup of the melted butter, 2 teaspoons of the salt, and 1 teaspoon of the pepper with a fork until mostly smooth. Pour mixture into a lightly greased 13- x 9-inch baking dish.
Combine pecans, breadcrumbs, cheese, and remaining 1/2 cup butter, 1/2 teaspoon salt, and 1/4 teaspoon pepper in a medium bowl. Sprinkle pecan mixture in an even layer over potato mixture.
Bake, uncovered, at 350°F until topping is golden brown, 28 to 30 minutes. Sprinkle with parsley.