Preheat oven to 400 degrees F. Scrub potatoes and pierce all over with a paring knife or fork. Rub with olive oil and sprinkle with kosher salt, then place directly on the oven rack. Bake for 40 to 50 minutes, or until the potatoes can be pierced easily with a paring knife.
Remove from oven allow to cool until they are able to be handled. Slice in half lengthwise and remove the flesh and place in a medium bowl, leaving a ¼ inch border around the skin so the potatoes remain sturdy. Melt 2 tablespoons of the butter and brush on the empty potato shells and sprinkle with salt and pepper. Place the empty shells on a parchment-lined baking sheet and bake for an additional 7 minutes. Remove from the oven and set aside.
Meanwhile, place the remaining 2 tablespoons of butter in a small saucepan over low heat. Once it begins to melt, add the white parts of the scallion and stir to combine. Once the butter is totally melted, add the milk and continue to cook over very low heat. (Do not allow the mixture to come to a simmer.)
Once the milk mixture is warmed through, remove from the heat and pour over the potato flesh in the bowl. Add the cream cheese, sour cream, salt, pepper and half of the shredded cheddar cheese. Using a potato masher, mash the mixture until combined and nearly smooth.
Fill the empty shells evenly with the mixture, mounding any excess on top of each potato. Sprinkle the tops with bacon, and the remaining shredded cheddar cheese. Return to the oven and bake until the cheese is melted and the tops are golden brown, about 15 minutes. Sprinkle with remaining green scallions and serve immediately.