Preheat oven to 350 degrees. Grease and flour a 12x18x1 inch jelly roll plan.
In a large bowl melt together butter, semisweet chocolate, and unsweetened chocolate. Let cool slightly.
In a separate bowl stir together eggs, coffee granules, vanilla, and sugar. Add the melted chocolate, and stir to combine.
Add flour, baking powder, and salt. Fold in chocolate chips and walnuts if using.
Pour batter into the prepared pan.
Bake for 15 minutes. Rap the baking sheet against the oven racks to let the air out. Bake for an additional 15 minutes, or until a toothpick comes out clean. Be careful not to over bake.