Preheat the oven to 350°F (175°C).
In a large mixing bowl, whisk together the melted butter, light brown sugar, and granulated sugar until well combined.
Add the eggs one at a time, whisking thoroughly after each addition, until the batter becomes lighter in color. Whisk the sugar and eggs for at least 4-5 minutes to achieve crinkly brownie tops.
Stir in the brewed espresso and vanilla extract, mixing until smooth.
Fold in the cocoa powder, flour, espresso powder, and kosher salt. Mix until just combined, being careful not to overmix.
Prepare your baking pan by cutting a parchment paper sling slightly smaller than the width of the pan. Lightly spray the bottom and sides of the pan with vegetable oil-based spray, then place the parchment paper sling inside, smoothing it out so it adheres to the pan.
Pour the brownie batter into the prepared pan, spreading it evenly.
Bake at 350°F for 30-45 minutes, or until a knife inserted into the center comes out mostly clean.
Remove the brownies from the oven and allow them to cool completely in the pan. Once cooled, use the edges of the parchment paper to lift the brownies out of the pan.
Store brownies in an airtight container at room temperature for up to 5 days, although they are best enjoyed within the first 2-3 days.