Preheat the oven to 350°F.
In a large skillet, heat the oil over medium heat. Add the dill, scallions, and leeks, and cook, stirring occasionally, until soft and fragrant, about 10 minutes.
Add the spinach and cook, stirring occasionally, until heated through.
Season with salt and pepper.
Remove the pan from the heat and let cool slightly.
Place the ricotta, feta, Parmesan, and eggs in a large bowl and stir to combine.
Add the cooled spinach mixture, stirring to combine.
Brush a 9-by-13-inch baking dish with some of the melted butter.
Place 1 phyllo sheet in the dish and brush with butter. Repeat with 10 more phyllo sheets, brushing each with butter.
Spread the spinach mixture on top of the phyllo.
Top with the remaining phyllo sheets, brushing each with butter.
Cut into squares or diamonds, being careful not to cut all the way through to the bottom.
Bake for 1 hour, or until golden brown and crispy.
Let cool slightly before serving.
