Arrange two racks to divide the oven into thirds and heat the oven to 400ºF. Meanwhile, scrub 4 large sweet potatoes clean and pat dry. Let 2 ounces cream cheese and 1 tablespoon unsalted butter sit at room temperature to soften while the potatoes cook.

Place the sweet potatoes directly on the upper rack and place an aluminum foil- or parchment-lined rimmed baking sheet on the lower rack to catch any juices. Roast until tender and a fork pierces easily into the potatoes, about 50 minutes.

Remove the baking sheet from the oven and place on a wire rack to cool. Discard the foil or parchment. Place the baked potatoes on the baking sheet and let sit until cool enough to handle, about 10 minutes. Meanwhile, arrange a rack in the middle of the oven and heat the oven to 450°F. Thinly slice 3 medium scallions; set 2 tablespoons of the dark green parts aside for garnish. Grate 6 ounces sharp cheddar cheese on the large holes of a box grater (about 1 ½ cups).

Carefully, as the potatoes will still be hot, slice the top third lengthwise off of the baked potatoes. Using a spoon, scoop out the flesh from the remaining potatoes into a medium bowl, leaving a scant ¼-inch border to create potato shells. Return the potato shells to the baking sheet and sprinkle ¼ teaspoon kosher salt on the insides. Scoop out all of the flesh from the trimmed top third of the potato and add to the medium bowl; discard the excess skin from the top third.

Add the remaining scallions, cream cheese, butter, about two thirds of grated cheddar cheese (about 1 cup), ¼ cup sour cream, 1 teaspoon hot sauce, ½ teaspoon garlic powder, ¾ teaspoon kosher salt, and ¼ teaspoon black pepper to the sweet potato flesh. Mash until combined and mostly smooth. Taste and season with more kosher salt and black pepper as needed.

Generously fill each shell with the mixture. Sprinkle with the remaining cheddar cheese. Bake until the filling is hot and the cheese on top is melted, 15 to 20 minutes. Sprinkle with the reserved scallions and more freshly ground black pepper. Crumble 4 slices cooked bacon, if using, over the top.