Preheat the oven to 180ºC/350ºF/gas 4. Place all the syrup ingredients in a medium saucepan with 300ml of water and bring to a gentle simmer. Let it bubble away, stirring occasionally, for 15 minutes or until the liquid has reduced by a third. Leave to cool. (The syrup must be cool when it is poured over the pastry otherwise the pastry will go soggy.)
Blitz the nuts in a food processor until coarse, then tip into a bowl and stir through the cinnamon and cloves.
Melt the butter, using a little of it to lightly grease a 40 x 25cm shallow tin with a pastry brush. Gently unfold the filo and cover with a damp tea towel to stop it cracking.
Layer sheets of filo in the tin and brush each layer with melted butter. After 4 layers, scatter over half the nut mixture; repeat with 4 layers of filo, then the rest of the nuts. Top with the last 4 layers of filo, then generously butter the top. Cut into diamonds with a sharp knife – ensure the blade goes right to the bottom.
Bake on the middle shelf of the oven on a hot baking sheet for 30–35 minutes, or until golden brown and crisp, reducing the temperature to 170ºC/325ºF/gas 3 if the baklava looks as though it is browning too quickly.
Remove the baklava from the oven and spoon half the cooled syrup over the top. Leave for 5 minutes, then spoon over the remaining syrup. Allow the baklava to cool before removing the individual pieces from the dish with a palette knife.