Preheat your oven to 350°F (175°C). Grease an 8×8-inch baking pan with butter or line it with parchment paper, leaving a slight overhang on the sides to make the brownies easy to lift out later.
In a large bowl, whisk together the melted butter, granulated sugar, and brown sugar until the mixture is well combined and slightly smooth.
Add the eggs one at a time, whisking thoroughly after each addition. Stir in the vanilla extract and the pumpkin puree. Ensure the mixture is uniform in color before moving to the dry ingredients.
Sift in the all-purpose flour, cocoa powder, instant espresso powder, and salt. Use a rubber spatula to gently fold the dry ingredients into the wet mixture. Stop mixing as soon as no more streaks of flour are visible to keep the brownies fudgy.
Gently fold in the semi-sweet chocolate chips. This adds extra pockets of melted chocolate that pair perfectly with the coffee notes.
Pour the batter into the prepared pan and spread it evenly with your spatula. Bake for 30 to 35 minutes. You can tell they are done when a toothpick inserted into the center comes out with just a few moist crumbs attached.
Remove the pan from the oven and let the brownies cool completely on a wire rack. Slicing them while they are still hot can cause them to fall apart, so patience is key for the perfect square.