Gently sauté the leeks in the olive oil until just tender, remove from pan and add chicken pieces, quickly seal on all sides. Add mushrooms and cook for a further 2-3 minutes. Then add wine and thyme leaves to pan and cover closely, simmer for 15 -18 minutes until chicken is cooked with no pink showing.
Remove chicken from pan along with mushrooms, bring juices rapidly to the boil and allow to reduce slightly, then stir in the crème fraîche. Meanwhile cut chicken into medium sized dice and return to pan with all vegetables stir through and allow to cool.
Preheat oven to 200°C/180°C for fan assisted/Gas M 6. Unroll pastry and cut out 3 x 12cm/5" disc and 3 x 10cm/ 4" discs. (You will just achieve this from the sheet - do not worry if there are any small gaps around edges of discs.)
Lay large discs on a lined baking sheet, divide cooled chicken mixture between them, spreading evenly over pastry but leaving a border all round. Brush borders with beaten egg. Place the smaller pastry discs on top of filling, then bring up the sides of the base pastry to just cover the smaller pastry rims. Pinch the base pastry to seal and press gently onto 'lids'.
Brush all over with beaten egg. Make a small hole in top of each lid, bake 'pies' on baking sheet and bake for 18-20 minutes until golden brown. Serve hot or cold.
*Or make 2 larger pies using a 15cm/6" and a 10cm/4" cutter (or use a tea plate/ saucer/ upturned glass to cut around)
For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home and view the full Food safety at home video.