Buttermilk-Boursin Mashed Potatoes

Bring potatoes and cold salted water to cover to a boil in a large Dutch oven. Boil 20 to 25 minutes or until tender; drain. Let stand until cool enough to handle and peel. Preheat oven to 400 degrees F. Press peeled potatoes through a potato ricer or food mill into a large bowl. Lightly fold cheese, 4 tablespoons butter, and next 3 ingredients into potatoes. Stir in 1 3/4 to 2 1/4 cups buttermilk, stirring just until smooth and fluffy (do not over- mix). Spoon into a lightly greased 3-quart baking dish. Dot top of potatoes with remaining 2 tablespoons butter and cover with aluminum foil. Bake, covered, at 400 degrees F for 30 minutes. Uncover and bake 10 more minutes or until thoroughly heated. Sprinkle with additional chives before serving.