Preheat your oven to 350°F (175°C). This ensures that your brownies bake evenly.
Line your baking pan with parchment paper, leaving some overhang on the sides for easy removal later. If you prefer, you can simply grease the pan with a little butter.
In a medium saucepan over low heat, combine the unsalted butter, chopped semisweet chocolate, and instant espresso powder. Stir continuously until melted and smooth. Remove from heat and let it cool slightly.
In a large mixing bowl, combine the granulated white sugar, packed light brown sugar, and the slightly cooled chocolate-butter mixture. Mix well until fully combined.
Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract until everything is smooth.
In a separate bowl, whisk together the all-purpose flour, unsweetened cocoa powder, and salt. Gradually fold the dry mixture into the wet ingredients until just combined. Be careful not to overmix.
Gently fold in the semi-sweet chocolate chips, ensuring an even distribution throughout the batter.
Pour the brownie batter into the prepared baking pan, spreading it evenly. Bake for 20 to 25 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
Once baked, remove the brownies from the oven and let them cool in the pan for about 10 minutes. Use the parchment overhang to lift them out and cool completely on a wire rack before cutting into squares.