Put the flour and salt into the food processor. Cut the butter into small pieces, add them to the flour and pulse until it forms a breadcrumb-like texture.
Add the milk a little at a time and pulse until it comes together - it won't form a ball but will clump. If it doesn't, add a little more milk. If you use AP/plain flour you may need slightly less milk.
Remove the dough from the food processor, press it together and wrap in cling wrap/film. Chill for approx 30min.
After it has chilled, preheat the oven to 375F/190C.
Roll out the dough to about as thin as you are comfortable with (approx 0.1in/3mm). Upturn your baking dish/plate and use the edge to cut a circle for the top of the pie. Put this piece of pastry aside, piece the rest together to form roughly a circle and roll to join up then fill the base of your dish/plate and trim the edges.
Roughly chop the turkey/chicken and spread across the base of the pie. Scatter over the raisins.
Melt the butter in a small pan over a medium heat. Add the flour, stir and cook a minute until it becomes slightly nutty. Add the milk about ¼cup at a time, removing from heat as you add the first couple times and mix in before adding more. Warm the sauce, stirring constantly, until it starts to thicken. Add the cheese and egg, mix in well and cook a minute longer then remove from the heat. Pour it over the turkey/chicken and raisins.
Moisten the edge of the underneath pie crust with either water or milk then put the top that you set aside on top. Press down with your fingers to seal. Brush the top with milk to help it brown (optional) and cut a couple slits in the middle as vents.
Bake for approx 30 minutes until gently brown on top. Best served warm but also good cold.