For the syrup:
1. Place walnuts, pistachios and cinnamon into a food processor and process until coarsely ground. Set aside.
2. Make the syrup: in a small saucepan combine all the syrup ingredients and bring to boil. wait until the sugar is dissolves and simmer 4-5 minutes more. Let cool while you are making the baklava.
3. Preheat oven to 175C (350F).
4. Unroll phyllo dough and trim the sheets to fit your baking dish. cover with a damp towel to keep from drying out as you work.
5. Brush a 9-by-13-inch baking dish with some melted butter. Layer 8 sheets of phyllo in the dish, brushing each sheet with butter before adding the next (keep the remaining dough covered with a damp towel). Sprinkle half of the nut mixture over the dough. Layer 6 sheets of phyllo on top, brushing each with butter before adding the next. sprinkle with the remaining half of the nut mixture. Layer the remaining 8 sheets of phyllo on top of the nut mixture, brushing each with butter. brush the top sheet with extra butter.
6. Using a sharp knife cut into diamond or square shapes all the way to the bottom of the pan.
7. Bake for about 35-40 minutes or until baklava is golden and crisp.
8. Immediately pour the syrup over the hot baklava, let soak at least 6 hours or overnight at room temperature. Garnish with grated pistachios (optional).