Light the barbecue and prepare for indirect grilling at 150-160 degrees.
Melt the butter in a pan.
Put the pistachios and walnuts in a food processor and chop finely. This may well contain larger pieces.
Grease the baking tin with melted butter.
Cover the base of the baking tin with 10 sheets of filo pastry, brushing each layer of filo pastry with melted butter.
Once the 10 sheets are on the bottom, add the chopped nut mixture on top of the filo pastry. (keep a little nut mixture for garnish if desired)
Place the next 10 sheets of filo pastry on top of the nut mixture and brush each layer again with melted butter.
Now cut the baklava in the baking tin into small squares/rectangles.
Now sprinkle the sliced baklava once more with melted butter.
Place the baklava in the middle of the grill and bake for about 50 minutes. Check every 10 minutes and turn the baking tin if necessary so that the baklava is evenly colored.
In the meantime, put the sugar and water in a pan and bring to the boil to make a sugar syrup.
The baklava is ready when it is evenly browned on top.
Remove the baklava from the grill and pour the sugar syrup over the baklava, making sure there is sugar syrup everywhere.
Leave the baklava to cool completely before serving.
