Chop or grind the walnuts, almonds and pistachios very finely. Mix the nuts with the sugar, cinnamon powder and nutmeg powder.
Butter each layer of filo. After 6 lavers, add some nuts. Then, butter another 6 layers and add most of the nut mixture. Top with another 6 layers and the remaining nuts. Finish with 6 layers of filo.
Cut diamond shapes or squares from the tray before placing in the oven.
Bake for approximately 30 minutes at 180 °C until golden brown.
Once out, pour the syrup on the hot baklava and sprinkle some pistachios on top of each baklava square.