Mashed Potato Soufflé

Ingredients:4 tablespoons unsalted butter, plus more for baking dish 5 pounds russet potatoes, peeled and halved crosswise
1 cup milk
1/2 cup sour cream
4 ounces cream cheese, room temperature
Coarse salt and freshly ground black pepper
1 1/2 cups heavy cream
6 ounces sharp or extra-sharp cheddar cheese, grated on large holes of a box grater
3 tablespoons fresh chopped chives
Directions:

1. Preheat oven to 350 degrees. Butter a large shallow baking dish; set aside. Fill a large pot with 2 to 3 inches of water; set a steamer insert into pot and add potatoes to insert. Cover and steam potatoes until tender and easily pierced with the tip of a sharp knife, about 15 minutes. Pass potatoes through a ricer into a large bowl.
2. In a small saucepan, heat butter and milk over medium heat until butter is melted. Add milk mixture to potatoes, along with sour cream, cream cheese, 1 tablespoon salt, and pepper; fold to combine. Transfer potato mixture to prepared dish.
3. In a medium bowl, whisk heavy cream until medium peaks form. Fold in cheese and season with salt and pepper; spoon cream over potatoes, spreading evenly to cover. Transfer to oven and bake until potatoes are heated through and top is light brown, about 30 minutes. Let stand 10 minutes; garnish with chives and serve.