Sift the flour and salt into a large mixing bowl.
Rub the lard and butter into the flour until the mixture resembles breadcrumbs.
Add enough cold water to form a dough using a palette knife.
Knead the dough briefly on a floured surface, shape into a circle, wrap, and chill for 20 minutes.
Melt butter in a pan and stir in flour for two minutes over medium heat.
Whisk in the milk away from the heat and then boil until the sauce thickens.
Stir in the cream, mustard, and stock cube, then allow to cool.
Sauté sliced leeks in butter in a heavy pan.
Add apples, bacon, and chicken to the pan and cook for several minutes.
Preheat the oven to 200°C and assemble the chicken, tarragon, pepper, and sauce in a pie dish.
Roll the pastry into a rectangle larger than the pie dish.
Trim strips of pastry to create a rim around the dish using water to adhere.
Place the pastry lid over the dish, crimp the edges, and cut a hole in the center.
Brush the pastry with the egg wash and add decorations with remaining trimmings.
Bake for 25 to 30 minutes until golden.