Preheat the oven to 350 degrees. Line an 8-inch square baking dish with parchment paper. Coat with cooking spray.
Make the cookie dough by heating the butter in a saucepan over medium heat, stirring often, until melted. It will start to bubble, foam, and separate then will turn golden brown with a nutty aroma. Remove from the heat immediately and pour into a medium mixing bowl to cool for 5 minutes. Side Note: Watch the butter carefully while cooking because it can burn quickly & easily.
Whisk in both of the sugars, egg, and vanilla extract until smooth and creamy.
Combine the flour, salt, and baking powder in a small bowl; mix well.
Gradually add the flour to the brown butter mixture until just combined.
Add the chocolate chips and mix until combined. Set aside.
Make the brownie batter by heating the same saucepan over medium heat. Add the butter and melt it then stir in the cocoa powder until smooth and glossy.
Remove from the heat and whisk in the sugar. Add the egg and vanilla and whisk until creamy and smooth.
Combine the flour & salt together in a small bowl and mix well. Add to the batter until just combined. Add the chocolate chips and stir to combine. Add the chocolate chips and stir to combine.
Alternate the spooning of the brownie batter and the cookie dough into the prepared pan, gently smoothing the top.
Bake for 25-30 minutes or until the edges are firm and golden. Remove from the oven and sprinkle the top with a few more chocolate chips, if desired.
Cool in the pan for 30 minutes before removing. Slice and serve. Enjoy!