Ingredients 6 tablespoons unsalted butter, room temperature, plus more for dish 5 pounds Yukon Gold potatoes, scrubbed 1/3 cup sour cream 4 ounces cream cheese, room temperature 6 ounces raclette or fontina, grated (2 1/2 cups) 1/2 cup whole milk, room temperature Kosher salt and freshly ground pepper 1/3 cup extra-virgin olive oil 2 teaspoons minced garlic (from 2 cloves) 16 small whole fresh sage leaves, or 8 large leaves, coarsely chopped 2 tablespoons finely chopped fresh chives, for serving Preparation Preheat oven to 375 degrees, with racks in upper and lower thirds....