1. Place potatoes in a large pot and cover with about 3 inches of cold water. Cover pot and bring to a boil over high heat, then lower heat to maintain a simmer and cook until potatoes are fork tender, about 15 to 20 minutes.
2. Reserve 1/2 cup of the cooking water, then drain water from potatoes. Push potatoes through a ricer into a large bowl. Add butter, which should melt from the heat of the potatoes, and stir to blend. Alternatively, place potatoes in bowl and use a potato masher or an electric mixer on low speed to mash with butter.
3. In a small saucepan over medium heat, bring milk to a simmer. Add sour cream and salt and whisk to combine. Pour hot milk mixture over potatoes and stir to combine. Stir in pepper if using. If mixture seems too thick, add a few tablespoons of reserved potato water, as needed. Serve warm.
Source: Hannaford fresh Magazine, November - December 2014