Preheat the oven to 400 degrees F.
Scrub the potatoes and dry thoroughly. Drizzle the potatoes with olive oil, coating evenly. Bake the potatoes on a sheet try until the skin is crispy and the potatoes are cooked through, about 1 hour. Allow the potatoes to cool slightly on a wire rack.
Slice each potato in half lengthwise. Using the tip of a spoon, scoop out the flesh of each potato half and transfer to a mixing bowl. Leave about 1/4-inch of flesh lining each potato skin. Transfer the potato skins to the sheet tray and return to the oven for 8 minutes.
In the meantime, mash the potato flesh in a bowl with a fork and add the cheese, sour cream, half-and-half and butter. Stir in the scallions (reserving a few for garnish) and season with salt and pepper.
Remove the potato skins from the oven and increase the temperature to broil. Working carefully with the hot potatoes, use a spoon to evenly fill each shell with the mashed potato mixture and top with the additional cheese. Return to the oven until the cheese has melted and becomes spotty and the potatoes are crisp on top, 3 to 5 minutes. Garnish with the reserved scallions.