Prepare your 9x13 pan with parchment paper or Bakers Joy.
In a double broiler gently melt the butter and chocolates together
As soon as the mixture is melted, take off the heat and allow to cool.
Whisk together the flour, baking powder, salt and Cocoa in a bowl.
Beat the eggs with the sugar on high speed, until the mixture is very pale and thick, and ribbony.
Add the vanilla and beat to combine.
Gently mix in the cooled chocolate mixture into the eggs and sugar
Then mix in the flour mixture 1/2 cup at a time.
Bake at 350 degrees until the top surface is slightly puffed and uniformly dry, and the batter no longer jiggles when you shake the pan gently - about 25-30 minutes depending on how thick they are. They will sink a bit as they cool.
Beat the peanut butter and butter until smooth
Add the choco and a pinch of salt and beat again
Add the powdered sugar 1 C at a time to get out clumps into the mixture and beat until smooth