Keep in mind, the one trick here is to defrost your puff pastry in advance. It had been years since I'd last worked with puff pastry and forgot to remove it from the freezer the first time I planned to make this. I had to punt and try another day... so do remember to take out your puff pastry and spinach the night before and stick them in the fridge (or set on the counter about four hours in advance) so that they properly defrost!
Time: 25 min for two fillets, 40 min for four (assuming you only have space to cook two at a time)