• Preheat the oven to 335℉ (168℃). Prepare a 9x13 baking pan with nonstick cooking spray and parchment paper. Cut the parchment paper so that it extends up past the sides of the pan.

Brownie Layer

• In a mixing bowl, whisk together the all-purpose flour, dark or dutch-process cocoa powder, and salt. Set aside.
• In a microwave-safe bowl, combine the unsalted butter and light brown sugar. Heat the mixture in the microwave for 90 seconds until the butter is fully melted. Whisk the melted butter and brown sugar together until combined and smooth. Set aside.
• In the bowl of a stand mixer fitted with a whisk attachment or in a large bowl with an electric hand mixer, whip the granulated sugar and eggs on medium-high speed for 2 to 3 minutes until light and pale in color. The mixture should double in size and become a pale yellow.
• While mixing on low speed, very slowly pour the melted butter/brown sugar mixture into the egg mixture. Once all the butter/brown sugar mixture is added, add in the vegetable oil and vanilla extract and mix on low speed until combined.
• Add in the flour/cocoa mixture and mix on low speed until the brownie batter comes together. Do not overmix the batter. Scrape the sides and bottom of the bowl to ensure all the ingredients are well combined.
• Pour the brownie batter into the prepared baking pan and spread the batter evenly with an offset spatula. Set aside.

Chocolate Chip Cookie Layer

• In the bowl of a stand mixer fitted with a paddle attachment or in a large bowl with an electric hand mixer, cream together the unsalted butter, light brown sugar, and granulated sugar until well combined and smooth. Add in the egg and vanilla extract and mix until well combined.
• Add the all-purpose flour, baking soda, and salt. Mix on low speed until the cookie dough forms. Fold in 1 cup of the semisweet chocolate chips until well dispersed throughout the cookie dough.
• Use a spoon, small cookie scoop, or your hands to drop dollops of chocolate chip cookie dough over the brownie batter, distributing them evenly across the surface. Press the remaining ½ cup of semisweet chocolate chips into the cookie dough.

Baking the Brookie Bars

• Bake the brookie bars for about 45-50 minutes, or until a toothpick inserted into the center comes out with moist crumbs. The center of the brownies will be slightly underbaked and will finish baking as they sit in the pan. If the chocolate chip cookie layer begins to brown too quickly, loosely tent the pan with aluminum foil after about 30 minutes and continue baking until done. Cool the bars completely to room temperature before removing them from the pan and cutting into squares.