How to Make It
Preheat oven to 400°F. Pierce potatoes with a fork, and bake in preheated oven until tender, about 1 hour.
Cool slightly, and cut each potato in half lengthwise. Scoop out flesh, leaving a 1/4-inch-thick shell. Combine warm potato flesh, cream cheese, milk, and butter in a medium bowl, and mash with a potato masher until combined. Stir in spinach, bacon, onion, salt, pepper, and 1 cup of the cheese until well combined.
Divide spinach mixture among potato shells; sprinkle each evenly with remaining 1 cup cheese, and bake at 400°F until golden and bubbly, about 15 minutes. Top with sour cream and scallions.