spanakopita (spinach pie)

My 6th grader has been craving this since Greek Fest at her school.  She was so busy at her own booth she didn't have a chance to try the spanakopita and was sure to be her favorite sample.  My college kid made this for her and it is DELICIOUS!  My husband said it's the best he's had.  I have to agree that it's probably the best I've had too.

spanakopita (spinach pie) (adapted from tina's chic corner)
3 teaspoons olive oil
1 onion, finely chopped
3 packages (10 ounces each) frozen chopped spinach, thawed and squeezed dry
3 eggs
3 tablespoons dried parsley
2 tablespoons dried dill (we purposefully omitted; not everyone in the family likes dill)
3/4 teaspoon salt
3/4 teaspoon pepper
12 ounces feta cheese, crumbled
16 sheets phyllo dough, thawed (I couldn't find it so used puff pastry and just worked it differently)
3/4 cup butter, melted

Preheat the oven to 350 degrees.  Butter a 9x13 pan and set it aside.
In a skillet over low/medium heat add the olive oil and finely chopped onion and cook it until it is slightly browned.
Thaw the frozen spinach and squeeze out the water. Add the spinach to the skillet and stir.
Remove the spinach mixture from the heat and set it aside.  Let this rest to get to room temperature.
In a medium bowl, mix together the egg, parsley, dill, salt, pepper and feta cheese.
Add in the spinach mixture and stir everything together and set this aside.  Make sure the spinach mixture is not hot because you don't want to cook the egg.
Make sure that the dough is completely thawed (the puff pastry I used was refrigerated).
My directions with puff pastry:
Cut the rectangle into two pieces.  Use a rolling pin to roll each piece into 9x13.
Brush one rectangle with butter and place in the 9x13.
Pour spinach filling over the rectangle of dough.
Brush the other rectangle with butter and place over the spinach filling.
Bake in a preheated oven for 45-50 minutes or until the top is golden brown.
Let sit for about 5 minutes before serving.