01 -
Preheat the oven to 350°F (177°C). Line an 8×8-inch baking pan with parchment paper, ensuring an overhang for easy removal.
02 -
In a microwave-safe bowl, combine the melted butter, vegetable oil, and chopped bittersweet chocolate. Heat in 30-second intervals, stirring until smooth.
03 -
Add espresso powder and Dutch-process cocoa powder to the melted mixture. Whisk thoroughly to bloom the cocoa and deepen chocolate flavor. Set aside to cool slightly.
04 -
In a separate large bowl, whisk together powdered sugar, granulated sugar, and vanilla extract until the mixture becomes thick, glossy, and lighter in color, approximately 3 to 6 minutes.
05 -
Gradually stir the cooled chocolate mixture into the sugar and egg mixture until fully incorporated.
06 -
Sift in the all-purpose flour, cornstarch, salt, and gently fold them into the batter with a rubber spatula, taking care not to overmix.
07 -
Fold in semi-sweet chocolate chips and nuts, if desired, evenly distributing them throughout the batter.
08 -
Pour the batter into the prepared pan, smoothing the surface. Bake for about 25 minutes, checking around 23 minutes; the edges should be set and a toothpick inserted centrally should come out with moist crumbs.
09 -
Allow brownies to cool completely before slicing. For cleaner cuts, chill in refrigerator briefly and wipe knife between slices.