Vegetable Puff Pastry Pie

My recipe was based on this recipe:

5 medium-sized onions - I used three large ones
enough butter or oil to cover the bottom of a medium-sized shallow pan 
350g of any firm variety of mushrooms, or a mixture - I used Leek, Silverbeet and broccoli 
chopped thyme, lemon thyme or oregano (just enough to sit in the palm of your hand)
about 200g crème frache - I used mixture of cream, sour cream and yogurth
425g puff pastry 
a little beaten egg or milk to glaze the pastry

plus some blue cheese (optional)

Peel and roughly chop the onions and let them cook slowly with the butter or oil over a low heat for 20 minutes or so, until they are golden, soft and almost transparent. Tear or slice the mushrooms into large, bite-sized pieces and add them to the onions, adding a little more butter or oil if they soak it all up. Leave them to turn golden and tender but stir them from time to time so they do not stick and burn. Season them with the chopped herbs and stir in the crème frache, grinding in a little salt and pepper as you go. You want a mixture that is creamy rather than runny, so let it bubble for a minute or two to thicken.

Heat the oven to 200 C/gas mark 6. The pastry needs to be rolled into two rectangles about 35cm by 20cm (conveniently the same measurements as the ready-rolled frozen stuff). 

Put mixture into Pie dish. Cover with two slices of puff pastry that have been stuck together with water. 

Brush a little beaten egg, milk or even water on top of pastry sheet. 

Bake the pie until it has puffed up like a cushion and is the colour of honey. This should take about 25 minutes.