In a bowl, combine butter, brown sugar and coffee granules; blend well. Add eggs, vanilla and cooled coffee; stir.
In a separate bowl, combine baking powder, salt, flour and cocoa; add to butter mixture. Stir in walnuts and chocolate chips.
Pour batter into a greased 13"x9" pan and bake at 350° for 25 to 30 minutes. Allow to cool and cut into squares. Dust with powdered sugar before serving.