Onion Pie recipe

This is a little improvised recipe from a Moomin Finnish Cook Book I received for my birthday present from Judith (thanks!).
As a Japanese, any recipe book without photos are strange.. but somehow feeling like in the Moomin world in the book, and experiencing Nordic simplicity before inspire me and I picked this super easy pie recipe.
It's like a quiche, great for side dish or snack or lunchbox.
I was lazy to use the shortcrust pastry today.. but you can make it using oats and grated carrots into the base for adding more flavour. 
I can see many variations of this recipe with bacon, peppers and tomatoes etc

Ingredients:
Pie/short crust pasty (frozen or chilled)
2 large or 3 medium onions
oil
100ml cream
1 beaten egg
salt and pepper
120g grated cheese (Cheddar or Emmental)

photo 1

photo 2

photo 3

1: roll the pasty and put on the oven-proof dish (photo 1)
2: bake this for 5-8 min in oven 200 degrees, then take out (leave the oven at 200c)
3: slice the onion in strips and fry until transparant soft (just before it gets brown!) (photo 2)
4: mix cream, egg and cheese and season with salt and pepper
5: put softened onion in 2
6: pour this into pre-baked pasty dish and oven cook for 15-20 min until golden on top (photo 3)