• Preheat oven to 350 degrees F. Lightly grease with butter and line a 9x13 inch baking pan with parchment paper, leaving overhang on the sides. Tip: Greasing the bottom of the pan slightly helps the parchment paper stay in place.

Make the chocolate chip cookie dough

• In a bowl, whisk flour, baking soda, and salt until evenly combined. Set aside.
• In a stand mixer or using an electric hand mixer, beat softened butter with both sugars over medium-high speed, for 2 minutes, until light and fluffy. Lower to medium speed and mix in the egg and vanilla extract until evenly combined.
• Gradually, mix in the dry ingredients into the wet ingredients until evenly combined and no pockets of flour remain. Scrape the sides of the bowl as needed. Don’t overmix.
• Fold in chocolate chips using a rubber spatula. Set aside. There's no need to chill the dough.

Make the brownie batter

• In a large bowl, melt the 8 ounces of semi-sweet chocolate and butter in the microwave oven in 30-second intervals, stirring each time to combine. It should take about 1 minute and a half, or until it’s just melted. Don’t let it get too hot - it shouldn't be boiling, just slightly warm and melted. Tip: Don’t let the chocolate touch any water - it will seize.
• Gradually whisk the granulated sugar into melted chocolate while it’s still a bit warm. It should look a bit grainy.
• Then, mix in eggs, one at a time, as well as the vanilla and salt.
• Mix in the cocoa powder and flour, scraping the sides, until fully combined and no pockets of flour or cocoa remains. Do not overmix. Set aside.

Assemble and bake

• Dollop the brownie batter and cookie dough, alternating, onto the prepared baking pan. Carefully, smooth out the top with a rubber or offset spatula. The brownie batter and cookie dough should be in one single uniform layer. Tip: If there are large chunks of cookie dough on top, smooth it over with some brownie batter. Cookie dough browns quickly, so protecting some of it with brownie batter helps.
• Bake for 35-38  minutes until a toothpick inserted in the middle comes out mostly clean (a few moist and fudgy crumbs are fine). Try not to open the oven as it’s baking to prevent heat from escaping.
• Remove from oven and let it cool down in the pan for 20 minutes. Then, transfer to a wire rack and let cool completely. Cut brookies into about 18 squares. Enjoy!