In a saucepan melt the butter and sweat the leeks without browning for five minutes on a medium heat until soft and buttery. Add the cumin and cayenne pepper and cook for a further five minutes. Put onto a tray to cool.
In a bowl add the ground pork, leeks and season. Mix well and then divide into four balls. Cover with plastic wrap and put into the fridge until needed.
To make the pastry, mix the flour and salt in a bowl and make a well in the centre. Bring the water and lard to the boil in a saucepan then stir it into the flour with a wooden spoon to form a smooth dough. Divide into four portions and leave the pastry for 10 minutes to cool.
Lightly grease each individual pie pan. Place it on a baking tray.
Take two thirds of each quarter of pastry and on a lightly floured table, roll it to fit the pie pan and overlap the edge. Carefully press into the corners and allow it to just hang over the edge. Roll the remaining pastry into an circle for the lid. Repeat this process with the remaining portions of dough.
Fill each pie with the pork filling. Brush the pie edges with egg wash and place the lid on top. Pinch the lid edge and the top of the pastry edges together with your thumb to crimp the pie and create a seal. Trim the edge with a knife so no pastry is hanging over the edge.
Pre-heat an oven to 350°F Brush the top of each pie all over with beaten egg yolk, make a hole in the middle of the pastry lid and cook for one hour.
Remove from the oven and leave to cool. Once the pie is cold, refrigerate for two to three hours.
Follow the instructions for the gelatin and add to the stock to make a firm jelly and refrigerate. Once the pie is cold, check around the pastry for any holes and fill them with softened butter so that the jelly doesn't escape. Take the jelly/stock from the fridge, remove the layer of fat from the surface and gently reheat to melt the jelly. Pour the stock into the round hole in the top of the pastry until the pie is filled. Cool in the fridge until the jelly is set.