Preheat oven to 350.
Prepare a 9 x 13" baking pan with butter or cooking spray, then line parchment paper and butter or spray that as well.
In a medium bowl, whisk together the flour, salt and cocoa, set aside.
In a heat proof bowl put the chopped chocolate, the butter and the espresso powder.
Place bowl over a saucepan of simmering water.
Stir occasionally until the butter and chocolate are melted and well combined and smooth.
Turn the heat off and leave the bowl over the water.
Add both sugars and whisk until combined.
Remove the bowl from the water and let cool to room temperature.
Once chocolate mixture is room temperature, add 3 room temperature eggs and whisk until combined.
Add the last 2 eggs, whisk until combined.
Whisk in the vanilla extract.
DO NOT over-beat the batter or the brownies will be cake-like and not fudgy.
Sprinkle the flour mixture over the chocolate mixture.
With a rubber spatula, fold the flour mixture into the chocolate, until just a bit of the flour is visible.
Pour the mixture into the prepared pan and bake for 30 minutes.
ROTATE the pan after 15 minutes, then bake for another 15 minutes.
Bake only until a toothpick inserted into the center comes out with a few crumbs attached.
Let cool on a wire rack.
Remove from pan, cut into squares and enjoy!