You may use ready-made phyllo dough from the freezer section of your local supermarket in this recipe; keep it covered with a damp cloth so that it doesn't dry out and crack. Or for a 100% homemade pie, roll out your own, using the recipe below.
1-1/2 pounds frozen chopped spinach, thawed, drained, and squeezed dry
1 medium-size onion, chopped fine
1 bunch fresh scallions, chopped fine and sauteed until tender
2 tablespoons butter
1-1/2 pounds ricotta
1/2 pound feta
8 ounces cream cheese
2/3 cup olive oil
1/4 cup fresh chopped parsley
1/4 cup fresh mint
Kosher or sea salt
Freshly ground black pepper
Preheat oven to 400°. On the stovetop over medium heat, saute spinach, onion, and scallions in butter, until tender. Add cheeses, oil, eggs, parsley, and mint; mix well. Season with salt and pepper to taste.
To make the phyllo dough, mix water, lemon juice, vegetable oil, salt, and flour. If dough is sticky, continue adding flour until it forms a ball and doesn't stick to your fingers.
Using a rolling pin or pasta machine, roll dough out as thinly as possible. (If you're using a pasta machine, cut strips to fit through the opening; then roll through six times, starting at first setting and ending at sixth setting.)
Line a greased 9x13-inch glass baking dish with phyllo. Use at least 3 layers on the bottom, adding melted butter between layers. Make sure layers cover the sides of the dish and hang over the edges. Add spinach mixture. Fold hanging phyllo layers up and over. Add two or three more layers of phyllo over the top of the mixture, buttering between layers. (Note that if you're using ready-made phyllo, use 10 layers of dough on the bottom and 10 layers on top, buttering each layer as you go.)
Brush top with beaten egg and sprinkle with sesame seeds. With a knife, cut through just the top phyllo layer in squares. Bake 45 minutes to an hour, or until golden brown. Let cool before cutting.
1 cup water
2 tablespoons lemon juice
1/3 cup vegetable oil
Pinch kosher or sea salt
3-4 cups flour
1 stick butter, melted, plus extra for baking dish