To make syrup, combine the sugar, honey, lemon juice and zest, cloves and 180ml (3/4 cup) water in a saucepan. Bring to the boil over high heat, stirring until sugar dissolves. Reduce heat to medium and simmer for 3 minutes, then set aside to cool.
To make filling, process walnuts in a food processor until finely chopped (take care not to over-process or nuts will become oily). Transfer to a large bowl. Repeat with almonds, then add to walnuts with sugar and cinnamon. Combine well.
Generously brush base and sides of an 18cm x 28cm (3.5cm-deep) slice pan with butter. Unroll filo on a large chopping board and place prepared pan on top. Using a small, sharp knife, cut around pan all the way through the filo sheets. Discard trimmings. Keep filo covered with a clean, slightly damp tea towel to prevent the sheets drying out. Working with 1 filo sheet at a time, brush with butter, then place in pan. Repeat with 8 filo sheets to create 9 layers. Evenly scatter over half of the nut mixture.
Repeat buttering and layering with another 6 filo sheets, placing them over the nut filling. Evenly scatter over remaining nut mixture. Repeat buttering and layering with another 6 filo sheets, placing over the second layer of nut filling. Using your hands, press filo gently to compress slightly. Brush top well with butter.
Preheat oven to 160C fan-forced. Place baklava in the freezer for 10 minutes to firm (this will make it easier to score filo). Using a small, sharp knife, score the top few layers of filo in diamond shapes; to do this, score filo parallel to the short sides of the pan at 5cm intervals, then score it at a 45- degree angle to the first cuts at 5cm intervals. Bake for 35 minutes or until golden (cover with baking paper if the pastry is over-browning).
Pour syrup over hot baklava in pan, then stand for 2 hours or until the syrup is absorbed and baklava is cool.
Using a sharp knife, cut baklava into pieces along score marks to serve. Baklava will keep, covered with plastic wrap in the pan, in a cool, dark place for up to 1 week.