Preheat oven to 375 degrees. Place potatoes on a baking sheet. Prick top of each potato a few times with a fork, and bake until easily pierced with a paring knife, about 45 minutes. Remove from oven; let cool slightly, about 10 minutes.
Using a serrated knife, cut off top one quarter of each potato, slicing lengthwise. Use a spoon to scoop flesh into a medium bowl, leaving a 1/4-inch border all around. Set shells aside. Mash flesh with a fork until smooth. Add remaining ingredients, and stir until combined.
Refill shells with potato mixture. Cook until potato is soft and filling is lightly browned on top, 35 to 40 minutes. Remove from oven; serve immediately.