Sift the flour and salt together and place it in a  bowl. Dice the butter and rub in to the flour mixture with your finger tips until it look like bread crumbs and then add enough cold water and egg to bring the mixture together as a firm dough. Knead lightly and wrap the dough in a cling film. Chill for approx 1 hour.

Heat the oil in a pan, add onion, garlic and stir until it become transparent.  Add the chicken and cook it till the flesh turns whitish in color. Then add mushroom, carrot, celery, pepper powder, salt and stir well until the chicken becomes golden brown.  Remove from the flame and keep aside.

Melt the butter in a sauce pan, add flour and stir until the raw smell goes. Then pour milk and stir constantly and add chicken stock and pepper to this. Once it is thickened, pour it over the chicken and mushroom mixture and stir well.

Transfer this mixture to the pie dish and leave until it is completely cool.

Roll out the dough on a lightly floured smooth surface. Cover the pie dish with this crust and trim the edges nicely.

Brush the top of the dish with beaten egg (egg wash) and make three slits on the top of the pie to allow the steam to escape during baking.

Bake the pie in 200°c until the top becomes golden brown.  Remove from the oven and this is to serve.