Heat oven to 350 degrees. Sift together flour, cocoa, and salt. Stir in coffee, and set aside.
Beat butter until smooth. Add sugar, and beat well. Add flour mixture, and beat until combined.
Pat dough into an ungreased 8-inch round pan. Bake until firm, 20 to 25 minutes. Remove shortbread from oven, let sit for 5 minutes, then cut into wedges. Let cool completely. Sprinkle with confectioners' sugar before serving.