In a medium size frying pan brown the chicken pieces over medium high heat. Add the leeks. Once the leeks are soft add the soup and wine and sprinkle the cornflour over the top. Mix in. Simmer for about 20 minutes or until the mixture starts to really thicken.
Preheat oven to 180 degrees C.
Pour the mixture into a casserole dish and cover with the pie pastry. Use a fork to make 'breathing' holes in the pastry.
Bake in the preheated oven for about 30 minutes or until the pastry is brown. Let cool and serve.