To cook the chicken, place all the ingredients in a large stock pot and cover with cold water.
Bring the water up to a boil and lower the heat. Cover and allow to cook for 90 minutes.
When the chickens are cooked through, remove from the stock and set aside to cool before shredding the meat. Discard the bones and excess fat and skin.
Strain the stock to remove all the aromatics then strain again through a muslin-lined sieve. Place the stock in the fridge to allow the fat to rise to the surface and solidify so you can skim it off. You will then be left with a beautiful stock.
To make the pastry, combine the butter, flour and salt in the bowl of a food processor and pulse until the mixture resembles course breadcrumbs.
Add the egg yolks and with the motor running, pour in the ice water, spoon by spoon until the pastry comes together in a ball in the food processor (you might need more or less water, all you need is for the pastry to come together).
Remove the pastry from the food processor and wrap in clingfilm. Place in the fridge to chill for 30 minutes.
After 30 minutes, roll the pastry out and line the bottom and sides of an oven proof dish approximately 25-30cm in diameter (make sure you have a bit of pastry overhang at the top of the dish so you can crimp the shortcrust and the puff pastry together).
Place the pastry-lined dish back into the fridge to set until you’re ready to assemble the pie.
To make the filling, saute the onion, carrot and celery in a splash of olive oil until soft and fragrant. Add the garlic and fry for another 30 seconds.
Add the chicken meat, parsley, lemon zest and juice and set aside.
To make the sauce for the filling, melt the butter in a saucepan.
Add the flour and mix into a roux.
Slowly whisk in the stock until you have a smooth, rich looking sauce. Turn down the heat and allow to cook gently for 10 minutes.
Add the cream and season to taste.
Mix the sauce with the chicken filling and set aside.
When you are ready to make the pie, pre-heat the oven to 180°c.
Roll the puff pastry out a little thinner and cut into a shape suitable to top your pie. Reserve any off-cuts to cut out pretty shapes to decorate your pie for.
Place the prepared chicken filling into the chilled shortcrust pastry-lined dish.
Top with the puff pastry and crimp the edges.
Decorate with puff pastry shapes then brush with the beaten egg.
Place the pie in the oven and bake for 45 minutes until the pastry is golden brown.
Remove from the oven and allow to rest for 5 minutes before serving.