9 lg. Russet potatoes (6 to 6 1/2 lbs.), peeled and cut into lg. chunks
1 c. sour cream
6 oz. cream cheese, at room temperature
8 tbsp. (1 stick) butter, at room temperature
1/2 c. milk
3 tsp. onion salt
Salt and freshly ground pepper

Lightly butter 9x14 inch oval baking dish. Place potatoes in large saucepan and cover with cold water. Boil until tender, about 30 minutes. Drain. Using electric mixer, mash potatoes in large bowl. Mix in sour cream, cream cheese, 5 tablespoons butter, milk, and onion salt. Season with salt and pepper. Transfer potatoes to prepared dish. Can be prepared 2 days ahead. Cover and refrigerate.

Preheat oven to 400 degrees. Slice remaining 3 tablespoons butter. Place on top of potatoes. Bake until heated through and light brown, about 30 minutes. 12 servings.