Melt the butter, leaving it to brown slightly as this will add an extra level of nutty flavor to your baklava.
Place the walnuts and almonds into the bowl of a food processor and blitz until you have a coarse rubble. Transfer to a bowl and stir in the slivered pistachios, orange zest, salt, cinnamon and one-fourth of the melted butter. Mix well.
Brush a baking tray well with melted butter. Lay the phyllo out on a clear work surface near the pan. Line the pan with one sheet of phyllo and brush with melted butter. Continue in this way with five more sheets of phyllo, buttering each layer well.
Spoon the nut mixture over the top (don’t press down), then top with the rest of the phyllo sheets, buttering generously as you layer them.
Use a sharp knife to cut through the layers in parallel lines to make diamond shapes. Bake for 1 hour.
In a saucepan, add the sugar, honey, water, lemon juice and cloves. Bring to a boil, stirring to dissolve the sugar, then simmer for about 10 minutes, until syrupy. Remove from heat and allow to cool completely.
When the baklava is golden, remove from the oven. Once it has come to temperature, pour the syrup over the top of the baklava, and put back in the oven for 5 minutes.
Garnish with crushed pistachios. Remove and leave to cool completely, by which time it should have absorbed all the syrup. Run a knife along the lines to loosen them before removing pieces from the pan.