How to Make It
In a large pot, cover the potatoes with cold water and bring to a boil. Cover and cook over moderate heat until the potatoes are tender, about 20 minutes; drain. Press the potatoes through a ricer into a large saucepan set over low heat.
Meanwhile, in a small saucepan, combine the milk with 10 tablespoons of the butter and 1 tablespoon of salt and cook over moderate heat until the butter is melted, about 3 minutes.
Pour the hot milk over the riced potatoes and cook over moderate heat, stirring occasionally, until blended, about 2 minutes. Stir in the crème fraîche, the remaining 2 tablespoons of butter and the chives and cook until the potatoes are heated through, about 5 minutes. Season with salt and pepper, transfer the mashed potatoes to a bowl and serve.