Wash the spinach, cut it, sprinkle it with salt and rub it between fingers to get rid of the excess moisture. Heat oil in a saucepan and sauté the spinach, onions and leeks. Leave them to cook till are soft and liquid is absorbed. Take the saucepan of the heat, add the fennel, feta, eggs and pepper. Mix well till blended. Taste the mixture and add salf if needed (feta is already salty, so usually no need for extra salt). Preheat oven to 340oF. Oil well a baking dish and line the pastry leaves, brushing each well with the olive oil as you lay them. Make sure you have enough extra to cover the edges. Put in the filling, smooth its surface and sprinkle with sesame sees. Bake the pie for an hour and add the olives on top.
Enjoy!