Preheat the oven to 350 and place your oven rack on the center rack. Spray a 9x9 baking pan with non-stick spray and use the kind that is meant for baking. Spray it VERY well! Place a sheet of aluminum foil going one direction across the bottom fo the pan and secure on the sides of the baking dish. Place another sheet of aluminum foil going the other direction across the bottom of the pan. Spray the top side of the foil with the same baking spray, very well.
In a medium sized microwave safe bowl (I use a large glass cereal bowl) place the chocolates, butter and cocoa powder and microwave on high for 1 minute. Allow to rest in the microwave while you do the other steps.
Using a whisk, in a large bowl, whisk the eggs, espresso powder, sugar, vanilla and salt together.
Using a wooden spoon, mix the flour in with the eggs mixture. This takes some stirring - keep stirring until it is well mixed. Then, remove the chocolate mixture from the microwave and stir it together like crazy until it is smooth and add by small amounts (about ½ cup at a time) to the egg mixture, stir well. Keep adding the chocolate mix until all mixed in - make sure to use a rubber spatula to get all of the chocolate from the small bowl!! Once well mixed, pour into the prepared 9x9 pan and again, use the rubber spatula to make sure it all goes in!
Place on the middle rack of the oven and set timer for 25 minutes. The center will puff slightly and the sides will become crusty. Remove as soon as a toothpick inserted comes out mostly smooth. In my oven, this is exactly 25 minutes. Yours might differ slightly. If yours doesn't come out clean at 25 minutes, then continue baking and recheck every 2-3 minutes.
Cool on the counter/wire rack for as long as you can stand it before you HAVE to eat the brownies. At least 30 minutes would be good - but go with what you have to. Cover well with plastic wrap to save. Serve with ice cream and/or cold milk.