Preheat the oven to 350°F (175°C) and prepare a 9×9-inch baking pan by lining it with parchment paper and spraying it lightly with non-stick baking spray.

In a large bowl, sift together the all-purpose flour, baking powder, salt, cocoa powder, and espresso powder.

In a medium saucepan, combine the melted butter, oil, and 1/3 cup of the granulated sugar, and heat over medium until melted and smooth.

In a separate mixing bowl, whisk together the eggs, egg yolk, vanilla extract, and remaining sugar until well combined.

Gradually pour the warm butter mixture into the egg mixture while whisking constantly.

Fold in the sifted dry ingredients and chocolate chips using a rubber spatula until just combined.

Scrape the batter into the prepared pan and smooth the top evenly.

Bake for 28 to 30 minutes, until the edges are firm and the top is shiny and slightly cracked.

Allow to cool completely on a cooling rack before slicing into squares.