Thaw the filo dough according to package instructions if frozen. Ensure it is at room temperature before use.
Preheat your oven to 350°F (175°C).
In a bowl, mix the finely chopped walnuts, almonds, and pistachios.
In a separate bowl, combine the granulated sugar, ground cinnamon, and ground cloves (if using).
Brush the bottom and sides of a 9x13-inch baking dish with melted butter.
Place a sheet of filo dough in the baking dish and brush it lightly with melted butter. Repeat with 10 more sheets of filo dough, brushing each sheet with butter.
Sprinkle a generous amount of the nut filling over the layered filo dough.
Layer 10 more sheets of filo dough, brushing each sheet with melted butter as before.
Repeat steps 7 and step 8 until all the nut filling is used.
Cut the layered baklava into diamond or square-shaped portions using a sharp knife.
Place the baking dish in the preheated oven and bake for 45-50 minutes, or until golden brown and crispy.
While the baklava is baking, prepare the syrup. In a saucepan, combine water, honey, granulated sugar, lemon juice, and optional vanilla extract. Bring to a boil, then let it simmer for about 10 minutes until the syrup thickens slightly. Remove from heat.
Once the baklava is out of the oven, immediately pour the warm syrup evenly over the cut portions. Optional: Sprinkle lemon zest over the baklava.
Allow the baklava to cool completely in the baking dish, allowing it to absorb the syrup and soften.
Serve the baklava at room temperature and enjoy the sweet, nutty layers of this delectable dessert.