Greek spinach and cheese pie

150g butter

900g leeks, sliced and washed really well

6 tbsp extra virgin olive oil

500g onions, finely chopped

8 spring onions (both white and green parts), finely sliced

900g fresh spinach, weighed after the stalks have been removed, washed really well

6 tbsp flat-leaf parsley, chopped

6 tbsp dill, chopped

350g feta cheese, crumbled

125g Parmesan cheese, grated

4 eggs, beaten

9 sheets of filo pastry, 30 x 43cm (about one packet)

15g melted butter, for brushing

egg wash, made by beating 1 organic, free-range egg with 2–3 tbsp whole milk

flaky sea salt

freshly-ground black pepper

nutmeg