Preheat oven to 350 degrees F (175 degrees C). Line a 9×9-inch baking pan with parchment paper and spray lightly with non-stick baking spray.

In a large bowl, sift together the flour, baking powder, salt, cocoa powder, and espresso powder. Set aside.

In a medium saucepan, combine the butter, oil, and 1/3 cup of the sugar. Heat over medium heat, stirring frequently, until butter is completely melted. Remove from heat.

In a large mixing bowl, combine the eggs, egg yolk, and remaining sugar. Whisk until well combined.

Slowly pour the warm butter mixture into the egg mixture, adding it gradually while whisking constantly until completely combined.

Add in the dry ingredients and chocolate chips, and gently stir with a rubber spatula until just combined.

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

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

Place the pan on a cooling rack and cool completely before slicing.