Simply make a lovely rich pastry (I used 10oz plain flour, 5oz butter, most of a beaten egg - leaving a little for glazing - and enough cold water to bind lightly), line a baking tin and bake the bottom blind (use baking parchment and ceramic beans, then remove for a few minutes to "dry" the inside). Use only 2/3 of the pastry for this, rolling out the rest for the lid.
Meanwhile, cook off a chopped onion or two and maybe a few mushrooms in some oil and/or butter, seasoning well; add your leftover meat (chopped into chunks) and gravy, allowing to thoroughly heat through. Add whatever herbs or other flavourings you fancy.
When the pastry is cooked but not too brown, remove from the oven and put the meat mixture inside with a little of the gravy. Top with any cold filling you are adding (it helps keep the pastry lid cold before it goes into the oven - I used cold apple sauce in this version) and the pastry lid, using the remaining beaten egg to stick it down and glaze the top. Pop back into the oven until the lid is nicely browned and serve with your choice of accompaniments ... totally yummy!
NB Make sure you either eat it all at once, or have the rest cold ... DO NOT RE-HEAT MEAT FOR A SECOND TIME!!!
