Let filo thaw out (if frozen) thoroughly before opening, or it will stick together.

Thaw out spinach and squeeze out all the water you can. (You can cook and chop an equivalent amount of fresh spinach, but it's a big pain and it won't taste any different.)

Chop onions and brown in some butter or olive oil. Mix the spinach in with the onions. Add some ground pepper, if you want. I sometimes add some lemon juice, too, if I have some handy.

Beat eggs; crumble feta and mix with the eggs. Combine the onions and spinach with the mixture and mix well.

Butter a large (11in. x 15in.) baking pan. Put one leaf of filo down on the pan and butter it. Repeat until eight or ten leaves of filo have been layered, buttering between each layer.

Add the spinach mixture to the pan and fold the edges of the bottom filo layer over the top of the spinach. Repeat the filo layering on top. Cut away the excess filo from the edges. At this stage you can keep it in the refigerator until you bake it (e.g., overnight).

Bake at 350° for 45-60 min. or until golden brown. If you score the top layer of filo with a knife before baking, it will be easier to cut when you are done.

For thicker spanakopita, use a smaller pan or more filling.