1 tbsp lemon juice
1 tsp ground cardamom
200g/7oz mixed pistachios and walnuts, roughly chopped
2 tbsp granulated sugar
300g/10Β½fl oz granulated sugar
150g/5oz unsalted butter, plus extra for greasing
18 sheets ready-made filo pastry (unwrap and keep under a damp tea-towel until you are ready to use)