4 lb. russet potatoes (about 8 medium), scrubbed
2 Tbsp. extra-virgin olive oil
1 Tbsp. Diamond Crystal or 1¾ tsp. Morton kosher salt, plus more
1½ tsp. freshly ground pepper, plus more
12 oz. thick-cut bacon slices (about 8), cut into 1" pieces
12 oz. sharp white cheddar, coarsely grated (about 3 cups)
4 oz. cream cheese, cut into ½" pieces
1¼ cups heavy cream
½ cup (1 stick) unsalted butter, cut into ½" pieces
⅓ cup sour cream
1¼ cups finely chopped scallions (from about 1 bunch), plus more thinly sliced for serving
2 tsp. garlic powder
6 cups vegetable oil (optional; for frying potato skins)
Step 1
Place a rack in middle of oven; preheat to 375°. Peel 4 lb. russet potatoes (about 8 medium), scrubbed, reserving peels if making crispy potato skins. Cut potatoes into 1" pieces and arrange in a single layer on a rimmed baking sheet. Sprinkle 2 Tbsp. extra-virgin olive oil, 1 Tbsp. Diamond Crystal or 1¾ tsp. Morton kosher salt, and 1½ tsp. freshly ground pepper over and toss to coat. Tightly cover with foil and bake until potatoes can be easily pierced with a butter knife without any resistance, 60–75 minutes.
Step 2
Meanwhile, heat a dry large skillet over medium. Cook 12 oz. thick-cut bacon slices (about 8), cut into 1" pieces, , stirring often, until browned and crisp, 7–10 minutes. Using a slotted spoon, transfer to paper towels to drain. Let cool, then finely chop.
Step 3
Immediately transfer potatoes to a large bowl (leave oven on). Add bacon, 12 oz. sharp white cheddar, coarsely grated (about 3 cups), 4 oz. cream cheese, cut into ½" pieces, 1¼ cups heavy cream, ½ cup (1 stick) unsalted butter, cut into ½" pieces, ⅓ cup sour cream, 1¼ cups finely chopped scallions (from about 1 bunch), and 2 tsp. garlic powder. Using a potato masher, smash together until mostly smooth (some lumps are okay). Taste and season with more salt and pepper if needed.
Step 4
Transfer potato mixture to a large ovenproof rondeau, 12" skillet, or 13x9" baking dish, spread into an even layer, and place on a clean rimmed baking sheet. Bake until top is golden brown, 30–40 minutes.
Step 5
Meanwhile, if making the crisped potato skins, place reserved potato peels in a medium bowl and pour in cold water to cover. Soak 15 minutes, then drain and pat dry.
Step 6
Heat 6 cups vegetable oil in a large Dutch oven or other heavy pot fitted with a deep-fry thermometer over medium until thermometer registers 350°. Working in 2 or 3 batches, fry potato skins until crisp and golden brown, about 4 minutes per batch. Using a slotted spoon, transfer potato skins to a wire rack set inside another rimmed baking sheet to drain and immediately season with salt. Let cool.
Step 7
Top casserole with thinly sliced scallions and crisp potato skins (if using) just before serving.