In a kettle cover the potatoes with cold water and bring salted water to a boil. Simmer potatoes for 12 to 15 minutes, or until they are tender. Drain potatoes and force them through a ricer into a bowl. Stir in the butter, 2 egg yolks, salt, and the white pepper and let mixture cool for at least 20 minutes or up to 2 hours.
Preheat oven to 425 degrees F.
Transfer 1/4 cup of the mixture to a lightly floured surface, with lightly floured hands pinch off a piece the size of a marble, and reserve it. Roll the larger portion into a smooth ball, and drop it gently into one of the chilled molds. Make a shallow indentation gently in the top of the ball, form the reserved marble size portion into a smooth ball, and carefully place it in the indentation. In a small bowl combine the last egg yolk with the milk and brush the egg wash onto each of the "brioches" , being careful not to let it drip down the side of the mold. Bake on a baking sheet for 25 to 30 minutes, or until they are golden brown. Let them cool on a rack for 20 minutes. Loosen the edges with a metal skewer and invert to carefully remove from molds. They may be made one day in advance. Store chilled and covered, and reheat at 400 degrees F. for 15 minutes.
Recipe courtesy of Gourmet Magazine