Heat oven to Gas Mark 4, 180°C, fan 160°C.
Put drained spinach in a bowl, add ricotta, seasoning and nutmeg, mix well.
Lay out 4 pastry sheets and brush with butter. Place half the spinach mix along one sheet, cover with another sheet, roll into a long sausage and fold ends under. Carefully transfer to a buttered baking sheet, repeat with rest of spinach and filo.
Brush pastry and spinach rolls with butter, place in the oven and bake for 15 minutes. Reduce heat to Gas Mark 3, 160°C, fan 150°C, and cook for a further 15 minutes, until a light golden colour.
Remove and leave to rest for 5 minutes. Cut into 7cm (3in), slices and serve.