Start by preparing the cookie dough. In a large mixing bowl, cream together the butter, brown sugar, milk, and vanilla extract until smooth and creamy.

Add the egg to the creamed butter mixture and continue to mix until well combined.

In a separate bowl, combine the flour, salt, and baking soda. Gradually add these dry ingredients to the butter mixture and stir until fully incorporated.

Stir in the chocolate chips until they are evenly distributed throughout the dough. Set the cookie dough aside while you prepare the brownie batter.

Preheat your oven to 350°F (175°C) and grease a 13x9 inch baking pan with baking spray or additional butter.

In a 2-quart saucepan, melt together the chocolate and butter for the brownie batter over low heat, stirring constantly to prevent the chocolate from burning.

Once the chocolate and butter have melted together, remove the saucepan from heat and stir in the sugar, eggs, and vanilla extract.

In another bowl, mix together the flour, baking powder, and salt for the brownie batter. Gradually stir these dry ingredients into the chocolate mixture until fully combined.

Pour the brownie batter into the prepared baking pan, spreading it out evenly with a spatula.

Using a spoon or cookie scoop, drop large dollops of the cookie dough onto the surface of the brownie batter. You can create a pattern or drop them randomly, based on your preference.

Place the pan in the preheated oven and bake for approximately 35-40 minutes, or until a toothpick inserted into the center of the brookies comes out clean or with a few moist crumbs attached.