In a medium bowl, cream the butter and sugar together until smooth. Beat in the egg and vanilla until light. Sift together the flour, cocoa, baking powder, and salt. Stir the dry ingredients into the butter mixture and form into a thick dough. If the dough is soft, wrap it in plastic and chill for 1/2 hour. Preheat the oven to 375 degrees and butter a baking sheet. On a lightly floured surface, roll out the dough to about a 1/4 inch thickness and cut into shapes. Place the cookies on the prepared baking sheet, sprinkle with confectioners sugar, and bake for 15 to 20 minutes until the centers of the cookies are firm. With a spatula, transfer the cookies to a cooling rack.
These crisp chocolate wafers may be rolled out and cut into shapes suitable for any festivity. Store the cookies in a tin with a tight-fitting lid to keep them fresh. (Yields 18)
From the Moosewood Restaurant Low Fat Favorites, published by Clarkson N. Potter, Inc. 1996.