Place the spinach in a sieve then pour over boiling water from the kettle to defrost. Squeeze to remove excess water, then mix with the spring onions, garlic, feta and eggs. Add the nutmeg and season to taste.
Stir together the butter and oil and brush over the sides and base of a 20 cm (8 inch) springform cake tin. Unwrap the filo pastry and cover with a piece of damp kitchen paper until ready to use it.
Working quickly, brush 1 sheet with the butter mixture and arrange in the tin, letting the excess pastry hang over the sides. Brush another sheet with the butter mixture, turn the tin a little and arrange it in the same way. Repeat until the bottom and sides of the tin are completely covered.
Spoon the filling into the tin, then fold the pastry edges in to cover the filling, scrunching them up a bit as you go. Brush the top of the pie with a little more butter mixture and cook in a preheated oven, 200°C (400°F), Gas Mark 6, for 20–25 minutes until golden and crisp.