Peel the potatoes and rinse under cold water. Cut each potato into quarters and place in a 4 quart saucepan. Cover with cold water and bring to a boil. Add 1 teaspoon kosher salt then reduce the heat to a low boil. Cook until the potatoes are tender and easily pierced with a fork, about 12 minutes.
Meanwhile, heat the buttermilk and butter together in a small saucepan over medium heat until the butter has melted and the mixture is hot but not boiling.
Drain the potatoes and then add them back to the pan and warm over low heat for 1-2 minutes for the moisture to evaporate.
Use a ricer, potato masher or food mill to mash the potatoes. Stir in the buttermilk and milk mixture 1/3 cup at a time until the potatoes are the consistency you prefer.
Stir in the crumbled blue cheese and chives and season with kosher salt and freshly ground pepper to taste.
