14 tablespoons unsalted butter, softened and more for the pan

6 pounds yukon gold potatoes peeled and cut into chunks

2 tablespoons + 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

• Lightly grease a 9 inch by 13 inch baking pan
• In a large pot, bring the potatoes, 4 quarts water and 2 tablespoons salt to a boil. Boil potatoes until tender.  Drain.
• Mash potatoes with 10 tablespoons butter, sour cream, 1 teaspoon salt and pepper.  Mash in the chives. Taste and adjust seasoning. Spread potatoes into prepared pan.
• In a small bowl, combine 4 tablespoons butter, bread crumbs and cheese. Mix until it forms coarse crumbs.
• Heat the oven to 400 degrees. Sprinkle crumbs over the top of the potato casserole and bake until golden (30 to 40 minutes).