This recipe is adapted from Starting with Ingredients: Baking by Aliza Green. I love to make it in a 12-inch cake pan, but you can also make this in a 13 x 9-inch rectangular pan. It's most crispy when freshly baked, but you can also bake this savory pie in advance and reheat it for serving.
Squeeze the cooked mixed greens dry in a colander and transfer to a mixing bowl. Toss with the scallions, parsley,chives and season to taste with salt and black pepper. Blend in the eggs and feta.
Preheat the oven to 375 degrees F. Combine the melted butter and oil in a measuring cup and have a pastry brush on hand.
Brush the baking pan (either a 12-inch cake round or 13 x 9-inch rectangular baking dish) generously with the butter-oil mixture. Layer the dish with 8 sheets of phyllo, brushing each one lightly with butter, and fanning them out so that they cover the sides of the dish and overlap it by a couple of inches, like a pie crust.
Mound the greens mixture into the crust and lightly pat into an even layer. Arrange another overlapping stack of 8 phyllo layers on top, again brushing each one with the butter-oil. Roll up tightly the overhanging edges of phyllo and brush the top and edges with all of the remaining butter-oil. Use a single-edged razor blade or razor-sharp paring knife to score the top in a diamond pattern.
Bake the pie until deeply golden brown and very crisp, about 1 hour. Let stand for about 15 minutes before serving.
Defrost the phyllo dough still wrapped in the package at room temperature for about 2 hours or until pliable.
While working with phyllo, always keep unused sheets covered with plastic wrap to keep them pliable and avoid becoming brittle.