Preheat the oven to 350ºF.
Line a 8x8 inch square pan with parchment paper and spray with non-stick cooking spray. Set aside.
In a mixing bowl, combine the eggs, melted butter, buttermilk, brownie mix, cocoa powder and espresso powder (optional) and beat with an electric mixer on low until combined, about 1 minute.
Pour the brownie batter into the prepared pan. Spread evenly with a spatula.
Bake for 37-40 minutes or until a toothpick inserted in the center comes out clean.
Allow the brownies to cool. Remove the brownies from the pan using the parchment paper. Slice and serve.
