Variation: Butter a 9 by 13 inch baking pan, and spread 6 sheets of filo, brushing each with butter, on the bottom. Spoon the spinach filling over the filo, then cover with 6 more sheets of filo, buttering each sheet. Score the top 3 sheets with a sharp knife. Bake 40 to 45 minutes, or until top is golden, let stand 15 minutes, then cut into squares and serve warm.