Heat oven to 400°F and adjust the oven rack to the middle position. Place a cooking rack over a foil-lined baking sheet.
Lightly rub each potato with oil and sprinkle with salt & freshly ground black pepper. Place the potatoes, evenly spaced, on the rack over the prepared baking sheet.
Bake the potatoes to an internal temperature of 209°F or until fork tender (45 minutes-1 hour).
Remove the potatoes from the oven, and leave the oven on.
Once the potatoes have cooled on the rack 10 minutes, cut the potatoes in half crosswise. Leave a 1/8 inch-¼-inch thickness of flesh in each shell, and carefully scoop out the potato flesh into a medium-large mixing bowl.
Transfer the potato shells back to the prepared baking sheet and cook at 400°F for 10 minutes (this is so the shells can crisp a little and hold their shape after filling).
While the shells cook, mash together half the cheese, sour cream, buttermilk, half the butter, half the scallions, half the bacon lardons to the baked potato flesh until smooth. Season with salt & pepper and mix together.
Transfer shells from the oven and set the oven to broil. Fill the potato shells, mounding in the middle, with the mashed potato mixture and top with remaining cheese, scallions, bacon lardons and butter.
Broil until the cheese has melted and the potatoes are spotty brown and little crispy on top, approximately 5-10 minutes. Watch closely.
Allow the potatoes to cool 10 minutes and serve.