How to Make It
Preheat oven to 400°F. Rub potatoes with oil, 1 teaspoon of the salt, and 1/2 teaspoon of the pepper. Pierce all over with a fork, and place on an aluminum foil-lined baking sheet. Bake in preheated oven until tender, about 1 hour. Cool slightly, about 10 minutes.
Cut potatoes in half lengthwise, and carefully scoop out pulp into a large bowl. Set potato skins aside. Add butter to potatoes, and mash with a potato masher. Add whipping cream and sour cream, and stir until mixture is mostly smooth.
Cut potato skins into 1-inch pieces, and stir 1/2 cup into mashed potatoes. Stir in half of the bacon, 1/4 cup of the scallions, and remaining 1 1/2 teaspoons salt and 1/4 teaspoon pepper. Transfer mixture to a lightly greased (with cooking spray) 2-quart baking dish. Sprinkle top with cheese and remaining potato skin pieces.
Bake in preheated oven until golden and bubbly, about 20 minutes. Sprinkle casserole with remaining half of bacon and 1/4 cup scallions, and serve hot.