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
Great Value Extra Virgin Olive Oil 17 oz
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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