3 pounds medium russet potatoes, scrubbed
1 teaspoon extra-virgin olive oil
⅓ cup reduced-fat cream cheese
¼ cup sour cream
1 ½ cups whole milk
4 tbsp melted butter
1 ½ cups shredded sharp Cheddar cheese, divided
5 slices bacon, cooked and crumbled, divided
¼ cup thinly sliced scallions, plus more for garnish
1 teaspoon salt
1 teaspoon garlic powder
1 teaspoon ground pepper
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. 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, stir in butter. 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.