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.