Trim the roots from the English spinach, or if using silverbeet, remove leaves from tough stems. Wash leaves and drain well. Coarsely shred the leaves and tender stalks of the spinach and set aside.
Place the feta in a large bowl and coarsely mash with a fork. Add the ricotta, kefalograviera, eggs, breadcrumbs, nutmeg, pepper and oil. Mix with the fork to combine. Add the spinach and set aside while preparing the pastry case.
Preheat oven to 180?C.=2 0Lightly grease a 20cm x 30cm x 5cm deep baking dish.
Lay the filo out on a bench. Cover with a dry tea towel then a damp one to keep it from drying out. Line dish with a sheet of filo and butter the filo. Top with another sheet of filo and butter and continue until about half the sheets of filo are used.
Using your hand or a large metal spoon, gently mix the spinach filling until thoroughly combined. Pour into the prepared pastry base and spread evenly. Top with remaining filo, buttering each sheet, ensuring the final sheet is well buttered. Trim any overhanging pastry and tuck in the sides.
Use a sharp knife to mark pastry top into diamonds, allowing the knife to pierce the pastry once or twice to allow air to escape during baking. Sprinkle lightly with water and bake in preheated oven for 45 minutes to 1 hour or until well browned and set. Gently shake the pan and the spanakopita will slide easily when cooked. Cover with foil if over browning. Cool on rack for 15 minutes before cutting to serve.