These brownies are rich, creamy and smooth on the inside, and the outside is crisped to perfection.
Adjust the rack one-third up from the bottom of the oven and preheat the oven to 375 degrees.
Line a 9 x 13 x 2-inch baking pan with foil. Grease the foil with the 1 tablespoon of butter. The easiest way to do this is to add the butter to the foil-lined pan and place it in the hot oven for a minute or so. Then use a pastry brush -- or the butter wrapper -- to make sure the butter evenly coats the bottom and sides of the foil.
Melt the chocolate and 8 ounces of butter together in the top of a large double boiler over hot water on moderate heat -- or in a heavy saucepan over very low heat. Stir occasionally until the chocolate and butter are melted. Stir to mix, remove from the heat, and set aside to cool to room temperature.
In a large bowl, use an electric mixer to beat the eggs with the vanilla, salt, espresso, and sugar at high speed for 10 minutes. On low speed, add the cooled chocolate mixture and beat only until mixed. Then add the flour and again beat only until mixed.
Use a rubber spatula to scrape the batter into the prepared pan. Smooth the top.
Bake for about 35 minutes, reversing the pan front to back as necessary during the baking to ensure it bakes evenly. Cover loosely with foil for about the last half of the baking time to prevent over-browning. At the end of 35 minutes, the brownies will have a thick, crisp crust on top, but if you insert a toothpick into the middle, it will come out wet and covered with chocolate. And that's exactly what you want. They're done!
Remove the brownies from the oven and let them cool for at least a few hours. If you can, refrigerate them them overnight before cutting. A serrated knife will cut them easily.