1.Heat the butter in a large saucepan. Add the onion, celery and garlic, then saute for 3-4 minutes until softened and fragrant.
2.Whisk together the flour, gravy mix and water, stirring into the saucepan. Simmer for 5 minutes until thickened and smooth.
3.Stir in the chicken, roasted vegetables and peas, then stir well until coated with the gravy sauce. Allow to cool.
4.Preheat the oven to 180ºC and line a 23cm round pie tin with the pastry sheets, leaving some overhanging. Spoon in the pie filling and flatten slightly, then fold the pastry over to semi enclose the filling.
5.Mix the stuffing mix with the water and crumble it over the centre to cover any remaining filling. Spray lightly with oil and bake for 35-40 minutes until the pastry is browned.
6.Serve the pie sprinkled with fresh chopped herbs and dish up with a green salad.
This is a Sunday favourite in our house, usually involving the leftovers from a Friday or Saturday night roast. You can also freeze the stripped meat and vegetables from your roast to make the pie at a later date.