200ml milk infused with parsley stalks, cloves, onion
Mix flour, salt and butter till crumble consistency, add wet ingredients till just comes together then take out and finish by hand on bench till there are no lumps visable. Wrap it tightly in clingfilm and then rest at least 30 min in fridge or 15 min in freezer before use.
Slice the potatoes on a Japanese mandolin to 1/4cm thickness and set aside. In a large pot heat the cream, salt, pepper, garlic and herbs, bring up to a simmer and then add the potatoes and gently cook at that temperature for 3 minutes.
Line a baking tray big enough to fit the potatoes and cream with baking parchment and layer up the potatoes inside, ladling over the cream as you layer.
Cover with one more sheet of baking parchment and cook at 160c fan oven for 45 minutes, with a skewer check the potatoes are soft in the middle then remove the paper and turn up the temperature to 180c for 10 minutes to brown slightly.
Allow to cool to room temperature then add another sheet of parchment on top and gently press with 1kg of weight in a similar sized tray overnight in the fridge.
In a large heavy based pan, place sliced onion and salt, put on a low heat with the oil and cook slowly until caramelized and dark golden in colour.
Flip the potato out of the tray onto a chopping board, using the paper underneath to wiggle it out if necessary and cut into an equal amount of 50mm and 70mm discs with a set of plastic cutters.
Line small plastic cups (or tea cups if you don’t have them) with two layers of clingfilm and put one small disc of potato in the bottom, then a little grated cheese, a layer of caramelized onion and then one big disc to finish. Leave the cups in the fridge for 1 hour to set.
On a lightly floured bench roll out the short crust to 1/2cm thickness and then rest in the fridge for 30 minutes. Cut out 6 discs of dough 18cm in diameter and reroll remaining dough then repeat process and cut out six discs at 12cm diameter for the bases.
Turn out the moulded potato onto the smaller disc, brush a little of the egg wash around the exposed pastry and then wrap the larger disc of pastry over the top, sealing it to the base being careful not to trap any air as you seal. Use plastic cutters to trim the lip of the pie to a nice circle leaving a 1cm border all around.
Brush the pie all over (but not the underneath) with a thin coating of egg yolk and chill in the fridge for 30 minutes. Take out and brush again, this time chilling till the egg is just tacky but not dry.
Score the surface of the pie with a sharp knife being careful not to go all the way through it dock the pastry around the neck where the potato meets the lip with the tip of the knife to stop it rising there.
Place the pies on a sheet of greaseproof paper on a baking sheet and cook at 200c fan oven for 25 minutes or till temperature reaches 65c in the middle of the pie.
Melt the butter; cook the flour until a roux has formed. Leave to cool for a minute then slowly add the milk, beating until smooth, after each addition.
For the parsley sauce, cook parsley in boiling water for 30 seconds, refresh in iced water for 1 minute then squeeze until all moisture is gone. Puree parsley until smooth and mix though the white sauce, season well.