Heat a large frying pan and brown the turkey, bacon and sausages. Remove with a slotted spoon and put in the slow cooker pot.
Add the onion and white part of the leek and cook for a couple of minutes until softened.
Mix in the flour and then pour the stock in and bring to the boil.
Add the mixture to the slow cooker pot, sprinkle over the herbs and add the carrots and celery.
Cook on high for 6 hours - or longer if you're out of the house.
Remove the bone and any fat from the turkey and add the green part of the leek to the slow cooker.
Cook for a further hour.
Pre-heat the oven to 200C/400F/Gas 6.
Line a pie dish with shortcrust pastry and put in the fridge to cool for at least 30 minutes
Meanwhile, drain the stew mixture through a sieve, reserving the liquid to use as gravy later.
Put the drained stew into the pie case and then top with a layer of puff pastry, tucking the edges inside.
Score diagonal lines across the puff pastry lid to let air escape and brush with beaten egg.
Bake for 45 minutes or until browned and risen.