1. Pre-heat oven to 200°C.
In a pan, melt butter and add leeks, garlic and mushrooms.
Cook over a low heat for 6 minutes, or until leek is soft, but not browned.
2. Sprinkle in the flour and mix well, until the mixture is thick.
3. Stir in stock, cream and wine.
Add chicken and stir through.
Put mixture in a shallow 20 cm pie dish and set aside to cool.
4. Paint around the pie dish with a little milk.
Cover with pastry sheet and seal around the edges firmly.
Trim off any hanging pastry and decorate the edges with the back of a fork.
5. Make a few small holes to let out the steam, and bush the top of the pie lightly with milk.
6. Bake for 25 minutes, or until golden-brown and crispy.