Brush your baking tray with butter and layout the first layer of filo pastry. Brush with butter and then add your next layer of filo pastry. Repeat this another 3 times, leaving you with 5 layers of filo pastry. Add one fifth of the walnut mixture. Spread around evenly. Repeat this process another 4 times. 5 layers of pastry, brushed with bitter followed by walnuts. Lastly, finish with 5 final layers of filo pastry. On the 5th and final layer of filo, make sure it lines up on two side with the baking dish. Cut the excess pastry from the other two sides. Then cut the baklava into four long strips and then cut into diamond shapes by cutting diagonal. Brush with butter and bake for 60 minutes or until golden.