Preheat the oven to 200C, gas mark 6.
Mix the flour and salt together. Rub in the butter until it looks like breadcrumbs. Mix the egg with the lemon juice and 2-3 tbsp of cold water. Make a well in the centre of the mixture and pour in the egg mix. Use a knife to mix together and form a dough. If the dough is too dry add a splash more water.
Turn out onto a lightly floured surface and knead to form a smooth dough. Wrap in cling film and leave in the fridge to chill for at least 15 minutes.
Gently heat the oil and then cook the onion and garlic until soft. Transfer to a bowl. Add the frozen spinach to the pan and increase the heat. Cook, stirring often until all the spinach is soft and all the liquid released has evaporated. Add the spinach to the onion and garlic and leave to cool.
Beat two of the eggs with the cream cheese. Add the cheddar and chives, and then season with salt, pepper and nutmeg. Add to the cooled onion and spinach mixture.
Roll out 2/3 of the pastry not a 30cm circle and add to a lined 21cm loose bottom cake tin. Roll out the remaining pastry to a 24cm circle. Spread the filling over the base. Make 3 evenly spaced depressions in the filling. Crack the remaining eggs into each of the depressions.
Brush the rim of the pastry with egg wash and place a lid on top. Press the edges to seal. Trim off any excess pastry. Brush the top with egg wash. Make a steam hole in the centre of the lid. Bake for 50-55 minutes.
Can be eaten hot or cold.