Don't miss out on our special Christmas issue with free 2023 calendar - subscribe by 11 October!
Heat oven to 180C/160C fan/gas 4. Melt half the butter with the oil in a sauté pan. Add the onion and cook for 10 mins until softened. Remove to a bowl.
Add a few handfuls of spinach to the pan and cook for a few mins until it has wilted down. Remove from the heat and drain in a colander. Repeat until all the spinach is cooked. Press with the back of a spoon to remove any excess liquid. Now roughly chop and tip into the bowl with the onion. Stir in the nutmeg, ricotta, egg yolks, Parmesan and some seasoning and mix well.
Roll out one pack of pastry on a lightly floured surface to a 25 x 30cm rectangle, then lay on a large baking sheet. With the longest side facing you, pack the spinach mixture down the middle of the pastry, leaving a 5cm border all the way around. Brush the pastry all the way round with some beaten egg.
Roll out the second pack of pastry to a rectangle slightly larger than the first. Drape over the top and gently press down the edges to seal both pastry layers together. Trim the edges to neaten and crimp with your fingers, or seal down with a fork.
Brush all over with beaten egg and, if you like, lightly score the pastry with the back of a knife in a criss-cross fashion, making sure you don’t cut all the way through. Bake for 40 mins. Leave to rest for 10 mins before serving.