2) Melt together the butter, 450g of the chocolate chips and the unsweetened chocolate in a medium bowl over simmering water. Allow to cool slightly.
3) In a large bowl, stir (do not beat) together the eggs, coffee granules, vanilla and sugar. Stir the warm chocolate mixture into the egg mixture and allow to cool to room temperature.
4) In a medium bowl, sift together 150g of the flour, the baking powder and salt. Add to the cooled chocolate mixture.
5) Toss the remaining 340g of chocolate chips in a medium bowl with the remaining flour, then add them to the chocolate batter. Pour into the prepared baking tray. Spoon the peanut butter over the top of the chocolate mixture and using a knife, swirl it through.
6) Bake for 20 minutes, then rap the baking tray against the oven shelf to force the air to escape from between the tray and the brownie dough. Bake for about 10 to 15 minutes more or until a cocktail comes out clean. Do not overbake!
7) Allow to cool thoroughly, refrigerate, and cut into large squares.