Preheat the oven to 350 degrees. Spray a 9 x 9 baking dish with cooking spray. Set aside.

In a microwave proof dish combine the butter and chocolate chips. Heat for 30 seconds and stir well. Continue cooking in 15 second intervals, stirring after each interval, until the butter and chips are melted and well combined.

Pour the butter chocolate chip mixture into a large bowl. Add in the cocoa powder and vanilla and mix well.

Add in the sugar and brown sugar and mix well.

Add in the eggs and mix until well combined and smooth.

Add the flour and salt into the bowl and mix until just combined.

Pour the batter into the prepared pan. Bake for 35 minutes.

Remove from oven and cool completely, in the pan, on a wire rack.

Cut into 16 pieces and enjoy.