Preheat the oven to 220°C.
Set the potatoes directly on the rack in the center of the oven and bake until easily pierced with a fork, about 1 hour. Remove from the oven and turn the heat down to 200°C. Cut a slit in the top of the potatoes and carefully scoop out the flesh into a bowl, leaving the shells intact. Mash the potato lightly with a fork. Add the butter, sour cream, and 1/3 cup of the cheese, and salt and pepper to taste. Refill the shells with the potato mixture mounding it slightly.
Set the potatoes on a baking sheet, and bake until heated through, about 15 to 20 minutes. Sprinkle the tops with the remaining cheese and bake until melted, about 5 minutes. Serve immediately.