Pre-heat your oven to 350 °F. Line a half-sheet pan (about 13 x 18×1) inch with foil and grease with non-stick spray or a little butter.
Pour some water into a double boiler (or medium sized saucepan) and place over medium heat. If using a pot, cover with a medium-sized heat proof bowl. You'll use this to melt the chocolate and you want it hot, but not so that the boiling water hits the bottom of the bowl. Put the brownie chocolate and butter in the bowl and melt over medium-low heat. Whisk frequently to blend and avoid burning. When completely melted, add cocoa powder. Whisk thoroughly to combine. Remove from stove to cool slightly while preparing the other ingredients.
In another bowl, mix flour and salt; set aside.
In the bowl of an electric mixer, mix eggs, sugar, vanilla and coffee until combined and light in color.
Carefully pour the chocolate mixture into the egg mixture, mixing continuously to combine. Do this in batches so you temper the mix and don't cook the eggs with warm chocolate. Fold in the flour and mix until just combined.
Transfer to the prepared pan. Bake for 20-25 minutes, or an inserted knife comes out almost clean. Do not over-bake or you'll end up with tough brownies! Cool completely before preparing ganache.
Ganache: Place chocolate in a small heat-proof bowl; set aside. In a small saucepan, slowly heat cream until it just begins to boil. Pour over chocolate and let stand for about 30 seconds; whisk until chocolate is melted and mixture is blended. Add butter; mix until smooth. Chill briefly until thickened (approx 15 minutes). Spread over brownies & top with chopped nuts. Let stand at least 1 hour, then refrigerate at several hours (if you can) before cutting into servings.