Rinse the chicken in cold water and place it in a large pan.
Add the clove-studded onion, carrot, bay leaves, stock cube, and peppercorns to the pan.
Cover with water, boil, then simmer for 45 minutes to 75 minutes until cooked.
Rub cold butter and shortening into salted flour until the mixture resembles breadcrumbs.
Add cold water to form a stiff dough, knead gently, and chill for 30 minutes.
Remove chicken, reduce cooking liquid to 250ml, strain, and skim off fat.
Cut chicken meat into chunks while discarding skin and bones.
Blend the boiled onion and reserved stock until smooth, then mix with milk.
Melt butter, stir in flour, then gradually add the stock-milk mixture and boil while stirring.
Season the sauce and fold in the chicken meat before cooling.
Preheat oven to 220°C and line a 20-25cm pie plate with two-thirds of the pastry.
Add filling, cover with a pastry lid, and seal edges with beaten egg.
Decorate with pastry leaves, brush with egg, make a steam hole, and bake for 45 minutes.