Preheat oven to 190°C.

Place chicken stock liquid into a pot set over high heat. Bring to the boil, then reduce heat to low and simmer until stock is reduced by half.

Lightly grease 4 x 175ml deep custard, soufflé or pie dishes with baking spray.

Roll pastry on a lightly floured bench to 2mm thickness. Cut pastry to fit inside of pie dishes and gently push pastry into prepared pie dishes. Cut out rounds to form pie tops and cut a 5mm hole in the centre of each pie top.

Fill pie dishes with pork mixture to about ¾ full.

Brush underside of pastry tops with water and place on top of pies. Press edges together with a fork. Rest pies for 20 minutes in the refrigerator. Brush tops with the egg wash.

Place pies in oven and bake for 17-20 minutes or until pastry is golden brown. Cool.

Reheat reduced chicken stock and pour warm stock into a squeeze bottle with a small hole nozzle. Pour stock into the pie through the hole in each pie top. Place pies into the refrigerator until stock has jelled.

Refrigerate the pies for up to two days. Remove from refrigerator for 30 minutes before serving.

For the short pastry: Place flour, salt, and pepper in a food processor bowl fitted with a metal blade. Sprinkle butter over flour and process until it looks like fine breadcrumbs. Whisk egg yolk with cold water, and with the food processor running, pour the egg yolk mixture through the feed tube until the pastry forms a ball. Shape pastry into a disc, wrap in plastic wrap, and chill for 30 minutes before rolling out.

For the pork pie filling: Cut pork fillet into 1cm cubes. In a frypan, sear pork on all sides, then add onion and cook until onion is soft and pork is cooked. Toss in herbs, salt, and pepper. Cool the mixture before using as pie filling.