*Note: Semisweet chocolate should be coarsely chopped.
** Unsalted butter should be cut into small pieces.
In a double boiler, melt the chocolate and butter over simmering water.
Remove from the heat and stir in the vanilla. In a small bowl, gradually
whisk the warm chocolate mixture into the egg yolks. Cover and
refrigerate until firm, about 1 hour.
Shape level tablespoons of the chocolate mixture into balls and then roll
them in the cocoa. Refrigerate the truffles.
