Preheat oven to 375°.
Bake potatoes at 375° for 1 hour or until tender. Cool 10 minutes or until cool enough to handle. Cut each potato in half lengthwise; scoop out pulp, leaving a 1/4-inch-thick shell. Place potato pulp, buttermilk, and remaining ingredients in a large bowl; beat with a mixer at medium speed until well blended. Spoon about 1/2 cup potato mixture into each of 8 shells (reserve remaining shells for another use). Arrange stuffed shells on a baking sheet. Bake at 375° for 20 minutes or until thoroughly heated.