Pre-heat oven to 350 degrees
Coat a non-stick 9 x 9-inch baking pan with pan spray and line with parchment paper. Set aside.
Combine the dry ingredients: In a medium bowl, stir together the flour, cocoa powder, baking soda, and salt. Set aside.
In a large bowl, measure the granulated and powdered sugar. Whisk together. Set aside.
Add the vanilla extract, oil, eggs, and egg yolk. Mix on medium speed until it is silky and thick, about 3 minutes.
In a microwave-safe dish, heat the butter and tell it is melty and bubbly. About one minute. Pour the melted butter into the sugar mixture and mix on high speed for about one minute to help the sugar dissolve.
Add the vanilla extract, oil, eggs, and egg yolk. Mix on medium speed and tell it is silky and thick- about three minutes.
Add the flour, cocoa powder, baking soda, and salt. Mix until you can no longer see any dry flower spots. Fold in ⅔ cup of chocolate chips.
Pour the batter into the prepared pan. Bake at 350 degrees for 35-40 minutes or until the toothpick comes out clean, but moist.
Allow the brownies to cool completely before cutting into 9 equal pieces.