In a large bowl, add in the butter, brown sugar and granulated sugar. Beat at medium-high until everything is combined and mixture turns creamy.
Add in the vanilla, egg, and egg yolk and beat until fully incorporated.
Divide this wet mixture into two equal parts.
For the brownie dough: take one part of the wet mixture and add the flour, cocoa powder, baking soda and salt and mix gently to form dough. Finally, add the melted chocolate and the chocolate chips and fold them together. Set aside.
For the chocolate chip cookie: take the other part of the wet mixture and add in the flour, baking soda and salt and mix well. Add in the chocolate chips and fold gently. Set aside.
Cover both the dough and refrigerate for at least one hour.
Preheat the oven to 350 F and line your baking tray with parchment paper; set aside.
Take 1 T of brownie dough and 1 T of chocolate chip cookie dough. Roll them together in between your palms. Place them on the prepared baking tray. Keep at least a 3-inch distance between each cookie.
Bake for 13-15 mins in the preheated oven. Let the cookies cool for 5 minutes in the baking tray before transferring them to a wire rack to cool completely.