Mix flour, cocoa, baking soda, and salt; set aside
Cream butter well. Gradually beat in sugar until mixture is light and fluffy. Beat in egg and vanilla until well blended.
Stir in chocolate and nuts, gradually stir in flour mixture until well-blended, chill dough for 30 minutes or until firm enough to handle.
Shape into 18 balls using about ¼ cup dough for each. Place 4 inches apart on lightly greased cookie sheet; flatten to 3 & ½ inch diameter. Bake on middle rack in preheated 350º oven15 minutes or until medium firm to touch. Cool on sheet until firm; Remove to racks to cool completely.
To decorate, place a lacy doily on cookie; dust with confectioners sugar stirred through a strainer; remove doily. Store cookies lightly covered with waxed paper between layers. Makes 18.