Mashed Potato Casserole With Sour Cream and Chives


INGREDIENTS
14 tablespoons unsalted butter, softened, and more for the pan
6 pounds russet or Yukon Gold potatoes, peeled and cut into chunks
2 tablespoons plus 1 teaspoon salt
1 1/2 cups sour cream
1 teaspoon black pepper
6 tablespoons finely chopped chives
2/3 cup bread crumbs
2/3 cup grated Parmigiano-Reggiano cheese

PREPARATION
Lightly grease a  baking pan.
In a large pot, bring the potatoes,water and 2 tablespoons salt to a boil. Boil potatoes until fork tender, about 20 minutes. Drain.
Mash potatoes with 10 tablespoons butter, sour cream, 1 teaspoon salt and the pepper. (If you have a food mill or ricer, now is the time to use it; push the potatoes through and then gently combine them with the butter, sour cream, salt and pepper.) Mash in the chives. Taste and adjust seasoning, if necessary. Spread potatoes into the prepared pan.
In a small bowl, combine the remaining 4 tablespoons butter, bread crumbs and cheese.
 Mix together until it forms coarse crumbs.
Heat the oven to 200c. Sprinkle crumbs over the top of the potato casserole and bake until golden and crisp, 30 to 40