1. Preheat the oven to 200 degrees C
2. Heat oil in saucepan, add the mushrooms, adn fry for 5 mintues. Remove the musthrooms to a plate. Add the leeks to the pan and fry fro 2 miutes, stirring and remove to a plate.
3. Add the stock, wine, bay leaf, and carrots to the pan, bring to the boil, reduce the heat and simmer for a further 5 minutes. Add the chicken and cook gently for a further 5 mins. Remove the chicken and carrots to a plate.
4. In a small bowl, blend the cornflour with 4 tbsp of the stock mixture and stir until smooth. Pour into the pan and cook, stirring for 3 mins. until thickened. Season and remove from the heat.
5. Spoon the chicken, all the vegetables and the sauce into a deep 1.7 litere pie dish. Stir in the thyme.
6. Roll out the pasty on a floured surface to 5mm thick. Cut a pastry lid. Roll out the trimmings and cut a 1 cm strip of pastry around the rim. Dampen the strips.
7. Dampen the edge of the pie dish with water and press the strip of pastry around the rim. Dampen the strip.
8. Carefully lift the pastry lid and place over the top of the pie dish and firmly press it to the strip all around to seal. Crimp or flute the edges together if you like. Make a small slit in the centre of the pastry to allow steam to escape. Glaze the pastry with beatn egg.
9.Bake until golden and the pie is hot through, about 40 mins.