Heat the Oven - Set the oven rack to the center position. Preheat to 400ºF (204ºF). Place a wire rack on top of a foil-lined rimmed baking sheet and set aside.
Prepare the Potatoes - Scrub and rinse the outside of the potatoes with cool water. Dry with a towel. Pierce each potato with a fork 8 times, about ⅛-inch deep pricks all around. Evenly space the potatoes on top of the wire rack. Lightly brush olive oil over the surface of the potatoes. Sprinkle with salt.
Bake the Potatoes - Bake until the center of the potato pierces easily with a fork and registers between 200 to 205ºF (93 to 96ºC), about 60 to 80 minutes, depending on size. Meanwhile, cook the bacon.
Cook the Bacon - Add the bacon to a cold large cast iron skillet. Turn heat to medium and cook, stirring occasionally until crispy, about 10 to 12 minutes. Transfer to a paper towel-lined plate to drain. Reserve 2 tablespoons for topping.
Cool the Potatoes - Remove the potatoes from the oven and allow them to cool until cool enough to touch, 10 to 15 minutes.
Remove the Flesh - Slice each potato lengthwise down the center. Use a spoon to remove the flesh and transfer to a large bowl. It helps to place the potato in a paper towel for better grip. Make sure to leave about ¼-inch thick shell of flesh around the edges. There should be about 3 ½ cups of flesh. Set aside.
Bake the Potato Skins - Place the potato skins, cut side up, on the sheet pan on top of the wire rack. Bake for 10 minutes to help dry the skins.
Make the Potato Filling - Lightly mash the reserved potato flesh with the butter. Add 1 cup of cheddar cheese, sour cream, milk, ¼ cup of green onions, and bacon. Use a spatula to combine the ingredients.
Fill the Potato Skins - Fill each potato skin with about ½ cups of filling and shape it into a mound. Sprinkle about 1 tablespoon of cheddar cheese on top.
Broil the Potatoes - Broil until the cheese is melted, about 3 to 5 minutes.
To Serve - Top with reserved bacon, green onions, and black pepper.
Notes
Larger Serving Size: Select 12 to 14-ounce potatoes.
Make it an Appetizer: Use 5 to 8 ounces of smaller potatoes.
Storing and Reheating: Refrigerate covered for up to 3 days. Reheat one at a time in the microwave on the “high” setting in 30-second intervals until warmed through, about 1 to 2 minutes.
Freezing: Individually wrap potatoes in plastic, place them in resealable bags, and store them in the freezer for up to 1 month. To reheat, unwrap and bake at 350°F (177°C) on a wire rack or foil-lined baking sheet until warmed through, about 30 to 45 minutes, checking every 5 minutes.