Preheat the oven to 325°F and line an 8”x8” square baking pan with parchment paper.
In a large microwave safe bowl add the butter and semi sweet chocolate. Melt for 30 second increments, stirring in between until fully melted.
Add the oil and sift in the cocoa powder. Whisk until combined.
Whisk in granulated sugar and brown sugar. Add eggs and vanilla extract. Whisk until combined.
In a separate medium bowl, whisk together the flour, baking soda, corn starch and salt.
Add the dry ingredients to the liquid ingredients and fold/mix together until thickened and combined.
Pour the brownie batter into the prepared pan and bake for 36 minutes.
Allow to cool completely before cutting into. You may like to refrigerate the brownies before slicing if you like.