01 -
Preheat oven to 325°F and line an 8x8-inch baking pan with parchment paper, leaving an overhang for easy removal.
02 -
In a microwave-safe bowl, combine melted butter, vegetable oil, and chopped dark chocolate. Heat in 30-second intervals, stirring until completely smooth.
03 -
Whisk espresso powder and Dutch-process cocoa powder into the melted chocolate mixture to bloom the cocoa and intensify flavor. Allow to cool slightly.
04 -
In a separate large bowl, whisk together granulated sugar, powdered sugar, and vanilla extract until thick, lighter in color, and glossy, about 3 to 6 minutes depending on method.
05 -
Gradually add cooled chocolate mixture to the sugar and egg mixture, stirring until fully incorporated.
06 -
Sift flour, cornstarch, and salt over the wet ingredients. Gently fold using a rubber spatula just until combined, avoiding overmixing.
07 -
Fold in semi-sweet chocolate chips and toasted nuts if desired, distributing evenly throughout the batter.
08 -
Pour batter into prepared pan, smoothing the surface. Bake for 25 minutes, or until edges are set and a toothpick inserted in the center comes out with a few moist crumbs, checking from 23 minutes onwards.
09 -
Allow brownies to cool completely in pan. For cleaner slices, chill briefly in the refrigerator and wipe knife between cuts. Serve as is or with ice cream.