Nonsoggy spinich pie with frozen spinach The base recipe for my spinach pie (rough recipe I don't have a book) is 


500g spinach
250g Feta cheese
250g Cheddar cheese
1 bunch of spring onions
1.5 - 3 eggs (for binding)


Baked into 2 large pies, made with filo pastry. Cooked at 180-200C.

Originally I would make this by using cooking fresh spinach in water,
then carefully drying it with paper towel,
and combining that with fried spring onion.

However the fresh spinach was too expensive, so I refined it.
Changing to frozen, which I would put in the microwave,
then while it was defrosting, I chop up the spring onions and put them into the microwave with it.
I would not drain this or anything just combine with the other ingredients (in the same bowl I microwaved it in even!)
This was great it made delicious pie and was low effort.
You couldn't taste the difference.

However I wanted to make it more filling.
so I tried adding potato, it was good and very filling. However, my family thought it was less full of spinach and feta goodness. 
So my next approach was to double the amount of spinach and cheese. 
It is delicious and as expected each slice is twice as filling. 
I've tried that twice now and both times it has ended up soggy on the bottom.

What can I do about this?
Is it a matter of squeezing the water out of the defrosted spinach?
Or is there some other trick, like cutting a hole in the top of the pastry to let the steam out while it cooks.
With more spinach you need to wring the hell out of it, whether you start with fresh or frozen. Cook the spinach a bit so it starts to release its liquid, then squeeze it out with your hands doing small batches at a time. When you're done with that, put it in a clean tea towel, wrap it up and twist and wring. You'll get even more liquid. I'm surprised actually that you say that you didn't wring the spinach originally but didn't have a problem with sogginess. Spinach contains a boatload of water.

{edit upon further reflection}

I would even go further than wringing the spinach. To protect against sogginess, I would briefly sauté the spinach after wringing it. That would be a great opportunity to incorporate other complementary stuff like onions or garlic too.