Scrub potatoes with a vegetable brush under cold running water. Brush or rub each potato with about 1 teaspoon oil. Bake until tender when pierced with a fork, about 1 hour and 15 minutes.
Remove from oven and cool slightly. Reduce oven temperature to 350°. Cut each potato in half lengthwise and scoop out centers, leaving a shell about ¼-inch thick. Arrange shells on baking sheet.
In large mixing bowl, with paddle blade of electric mixer, or use a potato masher, mix scooped our potato and butter until blended. Add all remaining ingredients and beat or mash until smooth.
Refill the potato skins with all the mashed potato. Put stuffed potato halves on baking sheet and bake until tops are golden brown, about 13 minutes. To serve, sprinkle with Parmigiano-Reggiano cheese and chives.
Nutritional Analysis per serving: 439 calories, 9 g protein, 59 g carbohydrates, 20 g fat (40% of calories from fat), 46 mg cholesterol, 6 g fiber, 540 mg sodium.