Preheat oven to 350 degrees (F). Line a 9 x 13-inch pan with parchment paper, and spritz with non-stick baking spray. Set aside.

In a large bowl, whisk together the flour, cocoa powder, and salt. Set aside.

In the bowl of a stand mixer, on medium speed beat together the melted butter, brown sugar, and granulated sugar for 2 minutes.

Add the eggs, one at a time, and beat well after each addition. Mix in the vanilla extract and beat the mixture until well combined.

Stir in the dry ingredients and mix just until combined, then stir in the chocolate chips.

In a large bowl, whisk together the flour, baking soda, baking powder, and salt. Set aside.

In the bowl of a stand mixer, cream the butter, brown sugar, and granulated sugar together for 2 to 3 minutes, until fluffy. Add the egg and beat until incorporated. Stir in the vanilla extract.

Add the dry ingredients to the butter and sugar mixture and beat just until combined. Stir in the chocolate chips.

Spread the brownie batter into the parchment-lined baking dish.

Take a large spoonful of cookie dough and flatten with your hands. Lay the cookie dough on top the brownie batter. Repeat with remaining cookie dough until the brownie layer is mostly covered with the cookie dough. You don't have to be precise or smooth out the dough since it will spread as it bakes.

Cover the baking dish with aluminum foil to prevent overbrowning. Bake for 20 minutes then then remove the foil. Bake an additional 10 minutes then sprinkle the chocolate chunks over the top of the chocolate chip cookie layer, if using. Bake another 8 minutes, then remove and cool on a wire rack. The cookie layer may look a bit underdone, but it will firm up as it cools.

Cool completely before cutting into bars. Store leftovers in an airtight container at room temperature for up to 5 days.