Preheat the oven to 350 degrees F and line a 9 inch square pan with parchment paper.
In a small bowl, add the chocolate and butter. Place over a small saucepan of simmering water, and stir often until fully melted. Remove from the double boiler and allow to cool for a few minutes.
Meanwhile, in a large bowl, add the sugars, eggs, vanilla, and salt. Using an electric mixer, beat on high speed for about 3-4 minutes until the mixture has doubled in size.
While mixing on low speed, slowly pour in the chocolate butter mixture.
Once it is fully combined, add the flour, cocoa powder, and chocolate, and mix on low speed until fully combined.
Set aside as you make the blondie layer.