Twice-Baked Potatoes Casserole

Preheat oven to 400°F and line a large rimmed baking sheet with foil. Rub potatoes with oil and pierce all over with a fork. Place on the prepared baking sheet. Bake until tender, about 1 hour. (Alternatively, to microwave, pierce potatoes all over with a fork and place on a large microwave-safe plate, omitting the oil. Microwave on High until tender, about 20 minutes.) Let cool slightly, about 10 minutes.

Meanwhile, whisk cream cheese and sour cream together in a medium bowl until smooth; gradually whisk in milk until well incorporated.

Coat a 9-by-13-inch ceramic baking dish with cooking spray. Cut the potatoes in half lengthwise and roughly chop the halves. Place the chopped potatoes in a large bowl and, using a potato masher, mash until mostly smooth. Gradually add the milk mixture, stirring just until incorporated. Add 1/2 cup Cheddar, 1/4 cup bacon, scallions, salt and pepper; stir until well combined. Transfer the mixture to the prepared baking dish. Sprinkle with the remaining 1 cup Cheddar.

Bake until the cheese is melted and the edges are browned, about 25 minutes.  Sprinkle with the remaining bacon. Garnish with scallions, if desired.