Make the brownie batter: Melt the butter in a microwave safe bowl. Whisk in the granulated sugar, then the eggs and vanilla. Sift the flour and unsweetened cocoa into a separate bowl. Add the salt to this mixture. Stir this dry mixture into the butter mixture. Only stir as much as needed - we don’t want to over mix the brownie batter.
Make the cookie dough: Using a stand mixer with a paddle attachment, cream together the butter, brown sugar, and white sugar. Beat in the eggs and vanilla, until fluffy. In a separate large bowl, whisk together the flour, baking soda, and salt. Mix the flour mixture into the butter mixture until just combined. Then stir in the chocolate chips.
Preheat the oven to 350 °F (177 °C). Prepare a 8X8 inch baking pan by spraying with non-stick baking spray.
Assemble the brookies by scraping the brownie batter into the pan. Dollop the cookie dough evenly into the pan. Swirl the cookie dough into the brownie batter, just a little. Try to smooth the top.
Sprinkle on a few extra chocolate chips, then bake covered with foil for 40 minutes. Uncover and bake for another 10 minutes or until the cookie layer is fully set.
Notes
Both the cookie batter and the brownie batter are a bit thick so it’s a little tedious to swirl the layers together but it's simple to do with a butter knife or offset spatula! Or, if you don’t care about the swirl look, just add the cookie layer and spread out evenly across the top of the brownie batter for a simpler approach!