Line a 13x9x2-inch baking pan with foil; grease. Melt chocolate and butter in top of double boiler over hot water over medium heat, or in a 4- to 6-cup heavy saucepan over very low heat, stirring occasionally to mix. Remove from heat. In a large bowl beat eggs, extracts, salt, instant coffee and the sugar for 10 minutes with electric mixer at high speed. With mixer at low speed beat in chocolate mixture just until mixed. Add flour; beat only until mixed. Stir in nuts. Turn into prepared pan; smooth top. Bake in bottom third of preheated 425 deg F oven 35 minutes, reversing pan front to back after 15 minutes to insure even baking. When done, cake will have a thick, crisp crust but a pick inserted in the center will come out wet and covered with chocolate. Do not bake any longer. Let stand at room temperature until cool. Cover with a rack or cookie sheet; invert. Remove pan and foil; turn cake right side up. Let stand at room temperature 6 to 8 hours, preferably overnight, or refrigerate a few hours before cutting. Using a serrated knife, trim edges if too dark then cut cake into 16 huge, or 24 extra-large, or 48 small squares, wiping knife blade with a damp cloth after each cut. Wrap individually or store in an airtight container with waxed paper between layers.