For the syrup, boil 600g of sugar, 400ml of water, the zest of 1 lemon, and 1 cinnamon stick for about 2 minutes, until the sugar dissolves. Off the heat, stir in 80g of honey and let cool completely.
Preheat the oven to 300°F / 150°C. Mix 500g of chopped walnuts with 2 teaspoons of ground cinnamon and 2 teaspoons of ground cloves.
Brush a 15 × 12in / 40 × 30cm baking pan with some of the 300g of melted butter. Layer in 10 of the 25 sheets of phyllo dough, brushing each with butter, then spread over the walnut mixture.
Top with the remaining sheets, brushing each with butter. Refrigerate for 15 minutes, then cut all the way through into pieces.
Bake on the lower rack for 1½-2 hours, until crisp and golden. Slowly pour the cold syrup over the hot baklava and leave until absorbed.
