Line a 13x9x2" pan with foil. Grease. Melt chocolate with butter in top of double boiler over hot water and medium heat. Beat eggs, extracts, salt, coffee, and sugar for 10 minutes at high speed. At low speed, beat in chocolate until just mixed. Add flour; beat just until mixed. Stir in nuts, if you are using them. Bake at 425 degrees for 35 minutes, reversing pan from back to front after 15 minutes. 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 and invert. Turn right side up. Let stand overnight (or refrigerate), then cut. Wipe knife blade after each cut.