Mix butter, salt, egg yolk and flour, lightly, knead with chilled water into a smooth dough, leave it for few mins to rest.
Make 2 portions of the short crust, roll one, put in a un-greased 8 inch pie plate pressing into and up the side of plate.
sprinkle with 1 tbsp flour, melt the butter in a medium sauce pan over medium heat, add chopped onion, cook for 2 mins, add in remaining flour, salt, pepper, mustard, gradually add in stock, honey, cook until thick, add in boiled chicken cubes and veggies.
spoon the chicken mixture into the crust lined pie plate, top with a remaining crust, flute the edges pressing to seal, decorate top as required.
Brush with beaten egg white and bake for 25 mins until golden brown.