Pre-heat oven to 200C (fan)
Spray bottom of medium sized saucepan with low fat cooking spray. Turn the heat up high, then down to medium when the oil starts to bubble.
Sauté leeks for approximately 2 – 3 minutes until softened
If using already cooked leftover turkey then add turkey, stir in with the leeks to heat through and add the condensed soup, the water, bring to the boil and allow to simmer for 2 minutes.
Otherwise if using uncooked turkey, then add turkey, stir in with the leeks and cook until no longer pink on the outside. Add the condensed soup. The water, bring to the boil and allow to simmer for 2 minutes.
Season the turkey leak and soup mixture to taste.
Roll out the puff pastry, cutting a lid big enough to cover the top of your pie dish.
Spoon the turkey leak and soup mixture into the pie dish and cover with the puff pastry lid.
Brush pastry lid lightly with the beaten egg.
Cook in the centre of oven until the pastry has risen and is lightly browned (approximately 15 – 20 minutes).
Remove from the oven and serve.