Preheat oven to 340 degrees F (170 degrees C).
To make the cookie dough, in a bowl cream Salted Butter (3 tablespoon) with Brown Sugar (2 tablespoon) and Caster Sugar (2 tablespoon) till combined. Then drizzle in Vanilla Extract (1 teaspoon).
Next, stir in All-Purpose Flour (1/2 cup) and Baking Soda (1/4 teaspoon) until it turns into a crumbly mixture. Mix in Semi-Sweet Chocolate Chips (1/2 cup) until well distributed. Set aside.
To make the brownie batter, in a large bowl, whisk in Salted Butter (1/3 cup), Brown Sugar (1/2 cup), Caster Sugar (1/4 cup) and Vanilla Extract (1 teaspoon) until well combined. Then add in Semi-Sweet Chocolate Chips (1/2 cup) and Unsweetened Cocoa Powder (1/4 cup).
Mix until the cocoa powder is well dissolved into the mixture. Then, crack in the Egg (2) whisk until just combined. Next, fold in All-Purpose Flour (1/2 cup).
Using a 7-inch square pan greased and lined with parchment paper, scatter 1/3 of the cookie dough mixture into the it. Then transfer all of the brownie batter into the pan. Scatter the rest of the cookie dough mixture ontop.
Bake it in the oven for 25 to 35 minutes.
Let it cool completely before serving. Once cooled, cut the brownie into squares.