Preheat oven to 325°F.
In a bowl, mix cocoa and flour.
In another bowl, mix sugar, butter, oil, and vanilla. Once well hydrated, gradually add eggs.
Toss the chocolate chips in a bit of cocoa.
Gradually mix the dry ingredients into the sugar and egg mixture. Finally, add the chocolate chips.
Pour the mixture into a deep rectangular baking pan lined with parchment paper.
Bake for a minimum of 35 minutes or until a toothpick inserted into the center comes out as clean as possible.