This is a very nice way to use up leftovers from a roast dinner. Use the amounts given in the recipe only as a guide. Chop and change the recipe according to the ingredients you have on hand. If you prefer shortcrust pastry then that is fine too. I often use the leftover gravy instead of the stock, I do water it down somewhat When I have less time I just cut the pastry into squares and make them as triangles.