- Preheat oven to 350°F. Spray an 8-inch square baking pan with cooking spray and line it with parchment paper long enough to allow the ends to extend over the pan. 
- In a large mixing bowl, add hot water and espresso powder. Whisk until the powder is dissolved. 
- Add melted butter, eggs, granulated sugar, and vanilla. Stir until the ingredients are incorporated. 
- In a separate bowl, whisk together the flour, confectioners' sugar, cocoa powder, and salt. 
- Add the flour mixture to the butter mixture, mixing until just combined. 
- Fold in ¾ cup of the chocolate chunks, reserving the rest for the topping. 
- Spread the batter into the prepared pan. Top with the remaining chocolate chunks. 
- Bake the brownies for 20-23 minutes. Brownies are done when an inserted toothpick is removed with crumbs but not wet batter. 
- Let the brownies cool in the pan before transferring them to a wire rack to cool completely.