chewy fudge brownies

1. Preheat the oven to 350°F (180°C). Lightly coat an 8- x 8-inch (20.5 x 20.5cm) baking pan with cooking spray. Optionally, line the bottom of the pan with parchment paper if the pan isn't nonstick. 2. In a medium bowl, whisk together the granulated sugar, brown sugar, and melted butter until combined. Add the eggs, egg yolk, vanilla extract, and vegetable oil. Whisk until thoroughly combined. 3. Stir in the fine sea salt, baking soda, and cornstarch. Add the all-purpose flour and cocoa powder, and stir until thoroughly combined and homogeneous. Fold in the chocolate until evenly distributed. 4. Transfer the mixture to the prepared pan, and use a spatula to spread the mixture evenly to the edges of the pan. Bake for 25 to 30 minutes or until the brownies are cooked through and a toothpick inserted into the center comes out clean. 5. Remove the brownies from the oven, and set aside to cool completely before cutting and serving.