Peel potatoes and rinse under cold water. Cut each potato into quarters and place in 4-quart saucepan. Cover with cold water and bring to boil. Add 1 teaspoon kosher salt; then reduce heat to low boil. Cook until potatoes are tender and easily pierced with fork, about 12 minutes.

Meanwhile, heat buttermilk and butter together in small saucepan over medium heat until butter has melted and mixture is hot but not boiling.

Drain potatoes, return to pot and warm over low heat 1-2 minutes for the moisture to evaporate. Use ricer, potato masher or food mill to mash potatoes. Stir in buttermilk and milk mixture 1/3 cup at time until potatoes are consistency you prefer. Stir in crumbled blue cheese and chives and season with kosher salt and freshly ground pepper to taste. Garnish with additional blue cheese and chives.