Pre-heat the oven to gas mark 4.
Melt the butter in a pan with the oil. Finely chop the onions and then fry until soft.
Put these in a large mixing bowl for the time being and allow them to cool.
Taking half a bag at a time put the spinach into the pan and place on the lid.
Let the spinach wilt for 2mins before giving a stir around, placing the lid back on and letting it wilt for another 2 mins.
Remove the spinach from the pan and place in a colander.
Let it cool for a few mins before squeezing out as much excess liquid as you can!
Once squeezed dry chop finely and place in the bowl along with the onions.
Repeat this process until all of onion is wilted.
Stir in the nutmeg, egg yolks, ricotta and parmesan.
Season well and give the mixture a stir until fully combined.
Roll out the first pack of pastry until it is as thick as a £1 coin and perfectly rectangle and place this onto a sheet of grease proof paper.
Spoon the spinach and ricotta mix onto the pastry leaving a border of roughly 3 inches.
Roll out the second pack of pastry so that it is larger than the first.
Brush the edges of the first pack of pastry with a little egg yolk and then lay the second pack over the top.
Take a fork and press the top piece of pastry into the second piece of pastry to seal it. (Alternatively you could crimp the edges by hand.)
Score the top of the pie in a large criss-cross pattern and then finally brush it all over with the last of the beaten egg.
Slide the pie onto a baking sheet and place in the oven to bake for 40-50mins or until golden brown all over.
Once it’s out of the oven let it rest for 10mins then serve while still warm.