Preheat the oven to 180°C.
Brush a 25cm x 18cm baking tray with melted butter.
Trim the filo pastry sheets to fit the tray.
Layer half the filo sheets into the tray, brushing each individual sheet with melted butter.
Mix the chopped walnuts and pistachios together in a bowl.
Spread the nut mixture evenly over the buttered pastry stack.
Layer the remaining filo sheets on top, buttering each sheet as before.
Score the top layer of pastry into a diamond pattern with a sharp knife.
Bake for 20 to 25 minutes until the pastry is golden.
Boil caster sugar, water, lemon juice, and ground ginger in a pan for 6 minutes to form a syrup.
Pour the warm syrup over the hot baklava and leave it to cool.
Whisk double cream, ginger syrup, ground ginger, and honey in a bowl until soft peaks form.
Fold the chopped almonds and stem ginger into the cream mixture.
Freeze the ice cream for two to four hours until set solid.
Serve two baklava diamonds per plate topped with a scoop of ginger ice cream.