Preheat oven to 375°F. Pierce potatoes with fork. Place potatoes directly on oven rack. Bake until potatoes are tender, about 1 hour 15 minutes. Transfer to baking sheet; cool 5 minutes.
Halve each potato lengthwise. Scoop flesh from potatoes, leaving 1/4-inch-thick shell; place flesh in large bowl. Add crumbled Roquefort cheese and sour creamto potato flesh; mash until smooth. Season mixture with salt and pepper.
Spoon potato mixture into 8 potato shells, mounding slightly and dividing equally (reserve remaining 4 potato shells for another use). Place potatoes on baking sheet. Sprinkle Parmesan cheese over potatoes. Dot with butter. (Can be made 1 day ahead. Cover and refrigerate.)
Preheat oven to 400°F. Bake potatoes until heated through and beginning to brown on top, about 25 minutes. Sprinkle parsley over potatoes and serve.