Wash spinach and chop very fine. (3 10 oz bags may be used in place of loose spinach). Sprinkle spinach with 1 tb. salt and allow to stand 15 minutes. Squeeze spinach to remove excess moisture. (This is an important step in making a good filling>) Combine with cheese, onion, eggs, olive oil, salt and pepper to taste. Arrange -10ºC ilo, which have been brushed with butter, in a greased pan (10 x 38 cm), each filo having been brushed separately. Cover with spinach filling. Cover with -10ºC ilo overall, brushing each with melted butter. Seal edges to retain filling. Brush top with melted butter. Bake at 180ºC or 45 minutes.