This twice-baked potatoes casserole has all the classic fixings in a creamy, smooth casserole. Leaving the potato skins on adds texture, while the bacon adds a little crunch. This crowd-pleasing casserole can be prepped ahead of time, making it perfect for your next big gathering.

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.

Prepare through Step 3, cover and refrigerate for 8 to 12 hours. Continue with Step 4, but bake for an additional 15 minutes.