Preheat the oven to 220C/425F/Gas Mark 7.
In a pan, over high heat, sauté the mushrooms with a little oil. Cook the mushrooms for 3 – 4 minutes then add the spinach and spring onions and season with some salt and pepper, cook for a further 2 minutes. Remove the contents of the pan to a bowl using a slotted spoon.
In a separate bowl combine the ricotta with two beaten eggs. Season with salt, pepper and nutmeg. Add the mushroom mixture to the ricotta and stir to combine (ensure there is not too much liquid in the mixture).
Place the filo pastry, sheet by sheet into a ovenproof dish and brush each sheet with a little butter. Place the ricotta and mushroom mixture onto the centre of the pastry and then fold the edge of the pastry inwards to create a crust.
Slide the pie on the hot plate and bake 25 to 30 minutes.