Ashley | Baker By Nature

Preheat the oven to 350 degrees (F). Line a 9×13-inch metal or aluminized steel baking pan with parchment paper. Spray lightly with non-stick baking spray and set aside.
In a large bowl, sift together the flour, cocoa powder, salt, baking powder, and espresso powder. Set aside until needed. 
In a medium saucepan, combine the butter, bittersweet chocolate, oil, and 1 cup (200g) of the sugar. Heat over medium-low heat, stirring frequently, until butter is completely melted. Remove from heat. 
In a large mixing bowl, combine the eggs and egg yolks with the remaining sugar (350g). Whisk until well combined, about 30 seconds. 
Slowly, pour the warm butter mixture into the egg mixture, adding it very gradually (a little bit at a time) and whisking constantly until completely combined. 
Add in the dry ingredients and chocolate chunks and, using a rubber spatula, slowly stir until just combined. *Do not over mix! Stop staring when you see the last trace of dry ingredients. Over mixing will give you cakey brownies. 
Scrape the batter into the prepared pan and smooth the top. Bake for 32 to 33 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 (at least 2 hours) before slicing.