To make the classic Greek dish spanakopita, mix cooked leeks, scallions and spinach with ricotta, feta and Parmesan cheese. Add two beaten eggs, and pour the mixture into a baking dish between layers of phyllo. Refrigerate until firm, brush with a beaten egg, and then bake until golden brown.
Cook 1/2 cup of finely chopped fresh dill, 6 chopped scallions and 2 small chopped leeks in a large skillet with 1/2 cup of olive oil over medium-high heat for 5 minutes. Add 3 pounds of frozen chopped spinach, season with salt and pepper, and cook for 2 minutes. Place the mixture in a large bowl in the refrigerator for 20 minutes. Add 16 ounces of whole-milk ricotta, 6 ounces of feta and 1/4 cup of freshly grated Parmesan cheese to the bowl. Stir in 2 lightly beaten eggs, and then refrigerate the mixture until ready to use.
Trim 20 sheets of phyllo dough to fit in a buttered 9-inch-by-13-inch baking dish. Layer 10 sheets of phyllo, brushed with butter, in the baking dish, keeping the remaining phyllo covered with plastic wrap and topped with a warm towel. Pour the spinach mixture into the dish, top with 10 more layers of phyllo, and then refrigerate until firm.
Cut the spanakopita into eight equal pieces, brush with top with a beaten egg, and then bake at 375 degrees Fahrenheit until golden brown.