Preheat oven to 350° F. Grease a 9″ x 13″ baking pan with cooking spray.
In a small bowl, whisk together flour, cocoa powder baking powder, and salt. This is the dry mixture.
In a stand mixer bowl, mix together melted butter, white sugar, and vanilla extract until it is well combined.
Add in the eggs one by one and mixing well after each addition.
Add the dry mixture, and mix until everything is just combined. Make sure to scrape the bottom and the side of the bowl, and use a spatula to do the final mix. Pour the brownie batter into the prepared pan. Set aside.
In a medium bowl, whisk together flour, baking soda, and salt. This is the dry mixture.
In a stand mixer bowl, beat together softened butter, light brown sugar, white sugar, and vanilla extract for about 3 minutes, until mixture is creamy.
Add 1 egg and mix it together for about 2 more minutes until the mixture is light and creamy.
Gradually add in the dry mixture into bowl and mix until the dough is combined.
Stir in the chocolate chips and chopped nuts.
Carefully spread the cookie dough over the brownie layer in the baking pan.
Bake in the preheated oven, about 20 to 25 minutes, or until a wooden toothpick inserted into the center of the brookies comes out clean.