2Melt chocolate with butter in a metal bowl set over a saucepan of simmering water, stirring until smooth.
3In a separate bowl, lightly whisk together eggs, walnuts, Sambuca, and granulated sugar.
4Stir in flour mixture and chocolate.
5Chill, covered, until firm, about 2 hours.
6Sift confectioners sugar onto a plate.
7Roll heaping tablespoons of dough into balls and roll balls sugar.
8Arrange balls 2 inches apart on lightly greased baking sheets and bake until puffed and cracked but centers are still a bit soft, 10 - 12 minutes in a 350 oven.