To make the béchamel sauce, melt butter in saucepan. Add flour and cook for 1-2mins. Gradually stir in milk. Add chicken stock pot. Bring to the boil for 4-5mins until mixture thickens.
Fry leeks in butter, add chicken breast pieces and chicken stock pot.
Combined chicken mixture and béchamel sauce and place into a casserole dish.
Place pastry on top and brush with whisked egg.
Bake for 1 hour in oven at 180C or until pastry is golden brown.
