In a medium saucepan over low heat, melt the butter and semisweet chocolate together until smooth.
Remove from heat and allow to cool slightly before stirring in the brown sugar and granulated sugar, followed by the eggs and vanilla extract; set aside.
In a large bowl, stir together the flour, cocoa powder, espresso powder and salt
Pour the chocolate mixture into the flour mixture, then stir until just combined
Fold in the chocolate chips, then wrap the bowl with plastic wrap and refrigerate for 4 hours.
For the Chocolate Chip Cookie Dough:
In a medium bowl, stir together the flour, baking soda and salt; set aside.
In the bowl of a stand mixer fitted with the paddle attachment, beat together the butter, brown sugar and granulated sugar until light and fluffy, about 3 minutes. Add the egg and vanilla and mix well.
Add the flour mixture in 2-3 smaller additions, mixing well after each addition.
Stir in the chocolate chips, then wrap the bowl with plastic wrap and refrigerate for 4 hours.
To Assemble and Bake Brookies:
Preheat the oven to 350°F/180°C or 160°C fan oven, line a baking sheet with parchment paper and set aside.
Get a heaping tablespoon scoop of the brownie cookie dough, and a heaping tablespoon scoop of the chocolate chip cookie dough and press them together, then roll between your hands to create one large cookie dough ball (the dough ball will be about 3 tablespoons of dough).
Place the cookie dough balls onto the prepared baking sheet 3” apart and press down slightly to flatten.
Bake in the preheated oven for 9-11 minutes, or until the cookies are just golden on the edges.
Allow to cool on the baking sheet for at least 5 minutes before transferring to a cooling rack to cool completely.
Notes
Keep Yourself Organized! You are making two completely different cookie dough recipes, so be sure to pay close attention to the ingredients and measurements while you’re mixing.
Chill the Dough. Both cookie doughs need to be very cold before baking so that they don't spread too much. At least four hours is ideal, but feel free to chill them overnight if you are starting the recipe in the evening.
Pay Attention to Placement. If you don’t put the dough on the sheet so that both colors are showing, you won’t be able to see both colors when the cookies are baked. Make sure that the seam between the two colors is at the top.
For soft, gooey centers, avoid overbaking your cookies. They will look slightly underdone when you take them out of the oven but will finish cooking as they cool on the baking sheet.
To Store: Brookies should be stored in an airtight container at room temperature. These soft cookies are best within 2-3 days, and will start to dry out after that.
Make Ahead: The cookie dough can be made ahead of time and stored covered with plastic wrap in the fridge for up to 2 days. Cookie Dough balls can also be frozen for up to 2 months.