2 pounds blue-fleshed potatoes (unpeeled)
1 cup whole milk
¼ cup (½ stick) butter
Place potatoes in large saucepan; cover with cold water. Bring to boil, reduce heat to medium, and simmer until tender, about 15 to 20 minutes, depending on the size. Drain well; cool slightly.
Peel and mash potatoes; place in large saucepan. Over medium heat, dry out potatoes for 2 minutes, stirring occasionally.
Meanwhile, heat milk in small saucepan until warm. Stir butter into potatoes. Add warm milk and stir until completely absorbed. Season with sea salt.