Preheat the oven to 350°F (180°C). Spray a 9x5 loaf pan well with nonstick cooking spray, line the pan with parchment paper leaving some overhang for easy removal, and set aside.
In a large mixing bowl, whisk the melted butter and sugar together until well combined. Then, whisk in the egg, egg yolk, and vanilla extract until fully combined.
Sift in the cocoa powder, flour, instant espresso powder, and salt. Whisk until just combined.
Scoop the batter into the prepared loaf pan and spread it around into one even layer.
Bake for 18 to 23 minutes or until a toothpick inserted into the center comes out mostly clean with just a few moist crumbs.
Remove from the oven and allow to cool completely in the pan on a wire rack. Once cooled, lift the brownies out of the pan, slice into 8 bars, and enjoy!
Notes
Storage Instructions: Brownies may be stored in an airtight container or ziplock bag at room temperature for up to five days.Freezing Instructions: Once the brownies have cooled completely, wrap the sliced brownies individually in plastic wrap, and freeze for up to 3 months. Thaw to room temperature before serving.