Heat 2 tablespoons of the oil in a large frying pan. Add the chicken and ham and brown the meat.
Sprinkle the flour over the browned meat and stir to coat.
Add the stock, bring to a boil to thicken and add the mixture to the slow cooker.
Add the remaining oil to a separate pan over medium heat. Stir in the leeks & onion and fry gently for two minutes, stirring occasionally until just softened. Add the carrots and cook for a further minute.
Add the chopped parsley and potatoes.
Season the mixture, to taste, with salt and black pepper.
Pour into the slow cooker with the sauce mixture.
Cook on low for 3 - 6 hours.
Preheat the oven to 400f˚/200˚c
Roll the pastry to about a ¼ inch thick (if not ready-rolled)
Separate the mixture into 4 individual casserole dishes (or one big one)
Cover each with pastry, crimp the sides, prick the center with a fork and brush with the egg wash.
Bake for 30 to 35 minutes or until golden brown.
Allow to cool slightly before serving (about 5 minutes).
Brushing the crust with egg wash will help to seal the crust and stop the filling from making the crust soggy.