2 1/2 pounds russet potatoes, peeled and cubed
1 1/2 cups milk
1 cup butter, softened
1 1/2 cups buttermilk
1. Preheat oven to 225°. Place potatoes in a large saucepan with cold water to cover by 2 inches. Bring to a boil over medium heat; boil 25 minutes or until potatoes are tender. Drain and spread potatoes in a parchment paper-lined jelly-roll pan. Bake 15 minutes.
2. Bring milk and butter to a simmer over medium heat. (Do not boil.)
3. Transfer potatoes to a large bowl. Add hot milk mixture; mash potatoes with a potato masher. Slowly add buttermilk, mashing to desired consistency. Add salt and pepper to taste.