Make the pastry in a food processor by adding the flour, salt, lard and butter and pulsing until mixture resembles fine breadcrumbs.
Then add 3 – 4tbsp of water and pulse until the mixture comes together to form a dough.
Knead the pastry on a floured board briefly before dividing into 2 flattened rounds for ease of rolling out later.
Cover with cling film and put in the fridge to chill for at least 20 minutes.
Pre-heat the oven to 200°C.
Meanwhile heat the oil in a large non-stick pan and fry the leeks gently for 5 minutes, then add the bacon pieces increasing the heat and cook for another 5 minutes. Finally add the chopped turkey and heat through for a further 5 minutes, put a lid on the pan to keep warm whilst you make pie base.
Once the pastry is chilled roll out one half to fit 21cm/8” deep pie dish (greased) and pat down inside and prick base all over with a fork.
Cut away excess pastry with the back of a knife and bake blind in the oven with a loose layer of foil over the top for 12 minutes
Then remove foil and return to the oven for a further 2 minutes to finish off.
Now make the roux sauce by melting the butter in a medium sized saucepan and add the flour stirring well with a whisk for a minute to form a paste.
Now off the heat gradually whisk in the milk bit by bit until it’s all added.
Return to the heat stirring constantly until the mixture coats the back of a spoon.
Then add the mustard powder, pepper and tarragon (no salt is needed due to the bacon).
Pour the sauce over the leek, turkey and bacon and stir well then place in pie base.
Roll out the second half of the pastry to form a lid for the pie.
Cut a strip of pastry (or a few) and line the rim of the pie dish to form a platform for the pie top.
Roll the pastry onto your rolling pin and place on top of the pie.
With the back of a knife cut away the excess pastry and crimp the edge of the pie, making a hole in the centre with a knife (to let out steam).
With the remnants of pastry make decorations, I like leaves but you can let your imagination go wild here!
Whisk up the egg and use a pastry brush to wash over the pie.
Bake for about 25 minutes on a baking tray until golden brown and cooked through.