Place a rack in the center of the oven; preheat the oven to 400 degrees F. Use a sharp paring knife to poke a few holes in each potato. Place the potatoes directly onto the oven rack. Bake until the potatoes are tender (a paring knife should easily slide in and out of the potato once it’s done), about 1 hour to 1 hour, 15 minutes. Use potholders to carefully remove the potatoes from the oven. Cool until the potatoes aren’t too hot to touch.
Turn the oven down to 375 degrees F. Line a large baking tray with foil and spray it with nonstick cooking spray.
Cut each potato in half lengthwise. Scoop out the potato flesh, putting it into a large bowl. Leave a border about ¼-inch thick for each potato skin. Arrange the potato skins on the prepared baking tray.
To the bowl with the potato flesh, add the butter, sour cream, heavy whipping cream, salt, and black pepper. Mash everything together until it forms a chunky mash. Stir in ⅔ of the shredded cheddar.
Scoop the potato mixture into the potato skins. Sprinkle the remaining ⅓ of the shredded cheddar on top.
Bake until the potatoes are warm throughout and the cheese is melted on top, about 15 to 20 minutes. To brown the cheese on top, broil briefly. Serve warm, topped with fresh chives.