Preheat your oven to 180ºC.
Slice your leek into thin rings and place in a pie dish with the butter and some salt and pepper. Cook for 20 minutes until the leeks are soft.
Add in the chicken (cut into chunks if you're using real chicken) and cook for another 15 minutes.
While this is baking, roll out your pastry to the same size as your pie dish.
Mix your cornflour in with your stock until smooth then add this to the dish with the sweetcorn, thyme and cream cheese. Give everything a good mix, then top with the pastry.
Use a fork to secure the pastry to the sides of the tin and cut a cross in the middle of the pastry to let steam escape.
Brush with a little melted butter then bake for around 20 minutes until golden and crisp.
