Espresso Chocolate Chunk Brownies

Preheat oven to 350 degrees (F). Line a 9×13-inch baking pan with parchment paper and lightly spray the paper, and any exposed pan, with non-stick baking spray. You can also butter the paper and pan if need be. Set aside.

In a medium bowl, combine the flour, salt, and cocoa powder; whisk well and set aside.
Place the semi-sweet chocolate, butter and instant espresso powder in a large bowl and set it over a saucepan of simmering water, stirring occasionally, until the chocolate and butter are completely melted and smooth. 
Turn off the heat, keeping the bowl over the water and add the sugar. Whisk until completely combined, then remove the bowl from the pan. The mixture should be room temperature.
Add the beaten eggs into the batter and whisk until just combined. Add in the vanilla. Do not overbeat the batter at this stage or your brownies will be cakey. Sprinkle the flour mixture over the chocolate mixture. Using a rubber spatula (not a whisk), fold the flour mixture into the chocolate until just a bit of the flour mixture is visible. Fold in the chocolate chunks.
Pour the batter into the prepared pan and smooth the top. Bake in the center of the oven for 30 to 35 minutes, rotating the pan halfway through the baking time, or until a toothpick inserted into the center of the brownies comes out with a few moist crumbs sticking to it.
Let the brownies cool completely in the baking pan, then lift them out of the pan using the parchment paper. Cut into squares and serve.