Serves: 20 large brownies
1. Preheat the oven to 180 C/Gas mark 4. Butter and flour a 30 by 46 by 2cm baking tray.
2. Melt together the butter, 450g of 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 140g of flour, the baking powder and salt. Add to the cooled chocolate mixture. Toss the walnuts and 340g of chocolate chips in a medium bowl with 35g of flour, then add to the chocolate batter.
5. Pour the batter into the baking tray. Bake for 20 minutes, then rap the baking tray against the oven shelf to force the air to escape from between the pan and the brownie dough.
6. Bake for another 15 minutes, or until a cocktail stick comes out clean. Do not overbake! Allow to cool thoroughly, refrigerate, and cut into 20 large squares.