• Preheat the oven to 350°F. Line a 9x13 baking dish with parchment or foil.

For the Brownies:

• Combine the melted butter and cocoa powder together in a large mixing bowl, and whisk together until the cocoa is fully dissolved. Add granulated and brown sugars and the salt, and whisk until the sugar is all moistened. Then whisk in the eggs and vanilla and beat well for about 1 minute. (The secret to glossy brownies is to beat the eggs and sugar very well!)
• Add the flour and mix together with a spatula until a few streaks remain, then fold in the chocolate chips, scraping the bowl down and mixing in any errant flour.
• Transfer the brownie batter to your prepared pan and spread into a thin layer, then set aside.

For the Cookie Dough:

• 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 3 to 4 minutes or until light and fluffy, stopping and scraping the bowl down as needed.
• Mix in the vanilla and egg and scrape the bowl down once more.
• Add the salt, baking soda, and powder then mix until combined.
• Pour in the flour and mix until almost combined. Then fold in the chocolate chips by hand with your spatula, reserving a handful to sprinkle on top later.
• Drop spoonfuls of the cookie dough onto the brownie batter. You don't need full coverage, it will be nice to see the brownie batter peaking through after baking.
• Cover the pan with foil and bake for 20 minutes. Carefully remove the foil, then bake for another 20 minutes uncovered. Allow the brookies to cool in the pan before removing them and cutting.