Roughly chop the walnuts in a food processor so they are in coarse pieces, not powder. Place them in a bowl and add the cinnamon, ground cloves, and lemon zest. This gives the filling its aroma.

Butter a large baking pan and lay down 3 buttered sheets of phyllo for the base. Start layering phyllo and walnut filling. Sprinkle the walnut mixture by hand, then cover with another sheet of phyllo, brushing each with butter. Repeat, alternating filling and phyllo, until you have about 12-14 layers, depending on how thick you want the baklava. Finish with 3 sheets of phyllo on top.

Cut the baklava into diamond shapes and stick a whole clove into each piece. Heat the butter (and oil, if using) until very hot, then pour it over the baklava to sizzle.

Bake on the lower rack of a preheated oven at 300°F (150°C) for 1 hour, then increase to 400°F (200°C) and bake for another 30 minutes.

Pour the hot syrup over the hot baklava.

Note: Of the 4 cups of butter, use about 2 cups melted for brushing the phyllo sheets, and the other 2 cups to heat and pour over the baklava before baking. If you prefer, you can use 1 cup butter and 1 cup olive oil. I like it this way.