Start by lining a 9x13 baking dish with parchment paper or aluminum foil, making sure to leave some overhanging bits for easy removal. Preheat your oven to 350°F (175°C) while you prep the batters.

In a large bowl, melt your unsalted butter in the microwave or on the stove. Once melted, stir in the cocoa powder until well combined. Next, whisk in both types of sugar and the salt. This step is crucial; the key to glossy brownies is really beating in the eggs and sugar. So, add in the eggs and vanilla extract, and mix vigorously until everything is well incorporated. Slowly sift in the flour, mixing until just combined. You want to see a few streaks of flour. Lastly, fold in the semi-sweet chocolate chips and your brewed coffee for an extra depth of flavor. Set this batter aside.

In a separate bowl, beat the room temperature butter and both sugars using a hand mixer on high speed for about 3-4 minutes, or until light and fluffy. This process helps give your cookies that sought-after airy texture. Once fluffy, add the vanilla extract and the egg, mixing again until everything is smooth. Now, sprinkle in the sea salt, baking powder, and baking soda; mix until these are just combined. Gradually add the all-purpose flour to the mixture, stopping just when you can no longer see any flour. Fold in the chocolate chips and include those walnuts if you like a bit of crunch. Reserve a small handful of chocolate chips for later.

Transfer the brownie batter to your prepared dish, spreading it out evenly. Now, drop spoonfuls of the cookie dough on top of the brownie batter, leaving some brownie visible; this will create that lovely ripple effect as it bakes. Sprinkle the reserved chocolate chips over the top, making it look extra inviting.

Cover the dish with aluminum foil and bake for 20 minutes. After that time, remove the foil and bake for an additional 20 minutes uncovered. Be sure to check doneness with a toothpick inserted into the center; you want it to come out slightly moist but not wet.

Allow the brookies to cool in the pan for at least 20-30 minutes before lifting them out using the parchment or foil overhang. Slice them into squares and serve. Enjoy!