Soften the leeks in the butter for a couple of mins. Add the spinach to the pan, cover and cook for 5-6 mins more until the spinach has sweated down.
In a separate bowl, beat the ricotta and eggs with the parmesan, spinach mix (cold), nutmeg and plenty of seasoning.
Layer the artichokes and tomatoes between the mix.
Heat oven to 180C/fan 160C. Line the base and sides of a greased 23cm clip-sided or loose-based tin with the filo pastry. Brushing each sheet lightly with the oil, place in the tin, oil-side down, leaving excess to hang over the edge. Turn the tin a quarter turn after each sheet.
Tip filling into the tin, fold excess pastry onto the top of the pie, a sheet at a time, crumpling to give a ruffled effect. Bake for 1½hrs until golden and firm.
