Brownie Layer

1. In a mixing bowl, whisk together the melted butter, granulated sugar, brown sugar, and unsweetened cocoa powder using a hand whisk or electric mixer until smooth.
2. Add the eggs and vanilla extract, and mix again just until combined.
3. Stir in the flour, salt, and chocolate chips using a spatula until fully incorporated.
4. Pour the brownie batter into a square pan lined with parchment paper and smooth the top with an angled spatula. Set aside.

Cookie Dough Layer

1. In a separate bowl, mix the melted butter with the granulated sugar and brown sugar using an electric mixer for 1–2 minutes until well blended.
2. Add the egg and vanilla extract, and mix again until smooth.
3. Add the flour, baking soda, baking powder, sea salt, and chocolate chips.
4. Gently fold the dry ingredients into the wet mixture using a spatula until you get a soft cookie dough.
5. Spoon the cookie dough over the brownie batter in the pan, and spread it gently with an angled spatula until fully covered.

Baking

1. Preheat your oven to 350°F (180°C). Bake for 30 to 35 minutes, or until the top is golden brown.
2. Check doneness by inserting a toothpick or knife into the center — it should come out with a few moist crumbs, not raw batter.
3. Let the brookies cool completely in the pan before lifting them out and placing on a cutting board.
4. Use a sharp knife to cut into 16 equal squares.