Preparation Steps

• Preheat oven to 325°F. Line a 9x13 inch metal baking pan with parchment paper with overhang. Spray lightly with non-stick baking spray.
• Prepare the brownie mix according to package directions by combining the required eggs, water, and vegetable oil.
• Pour the brownie batter into the prepared pan, spreading to an even layer. Set aside.
• In a separate bowl, beat the melted butter, light brown sugar, and granulated sugar on medium speed until fully combined.
• Add the egg, egg yolk, and vanilla extract to the butter-sugar mixture and beat until smooth.
• Add flour, cornstarch, baking soda, and salt. Mix on low speed until no dry flour streaks remain.
• Fold in the semi-sweet chocolate chips until evenly distributed.
• Using two spoons, drop dollops of cookie dough evenly over the brownie batter to ensure even baking.
• Cover the pan with aluminum foil and bake for 20 minutes. Remove foil and bake uncovered an additional 15-20 minutes until a toothpick inserted comes out clean or with a few moist crumbs.
• Remove from oven and let cool completely on the counter.
• Use parchment overhang to lift the brookie from the pan and cut into 12 large or 24 small servings.