• Preheat oven to 350°F. Line a 9×13-inch pan with parchment paper, then spray with non-stick baking spray. Set aside.

For the Brownie

• In a large bowl, microwave the butter for 1 minute, or until melted. Once the butter is melted, stir in the cocoa powder. Let the mixture cool for a few minutes so it doesn't scramble your eggs.
• Whisk in the powdered sugar, eggs, and vanilla extract until completely smooth and combined. Fold in the salt and flour just until combined (do not overmix), and pour into the prepared baking pan and set it aside.

For the Cookie

• In a large mixing bowl with a hand mixer or a stand mixer fitted with the paddle attachment, beat the butter, granulated sugar, and brown sugar on high for 1 minute or until slightly fluffy, stopping and scraping the bowl down as needed.
• On low speed, mix in the egg and vanilla extract just until combined. Add the salt, baking soda, and flour, then mix until combined. Then fold in the chocolate chips by hand with a spatula.
• Drop spoonfuls of dough on top of the brownie layer. Don’t cover the brownie batter completely; it will look good to have some brownie showing. Sprinkle a handful of extra chocolate chips on top before putting it in the oven.

Bake

• Bake for 26-30 minutes or until the cookie layer is light golden brown and the brownie edges are set. If the cookie dough begins to brown too quickly, place a piece of aluminum foil loosely across the top. Allow to cool completely for at least 30 minutes before removing them from the pan and cutting into bars, they’ll be too soft when warm.