1. Place the ham hocks in a large saucepan and cover with cold water. Bring to the boil and skim any scum off the surface.
2. Reduce heat to a gentle simmer and add the chopped vegetables, a teaspoon of chopped thyme and the black treacle. The treacle will take some of the saltiness out of the ham and give the stock a wonderful rich color. Simmer for 2-3 hours or until the meat is just starting to fall off the bones.
3. Remove the meat from the pan and allow it to cool. Strain the remaining stock into a clean pan and return to the boil until it has reduced by a third, then take the pan off the heat and leave to cool. This will become the jelly for the pie later on.
4. Pick the meat from the ham hock removing any fat and muscle. Flake the meat into a bowl and season with coarse black pepper and the freshly chopped thyme to your taste. Remember this is a cold pie so pepper will really bring out flavor once rested and chilled. Hocks can be very salty so do taste before adding any extra salt.
5. Next place the chicken between two pieces of cling-film and batter out with a rolling pin to tenderise and season with salt & pepper.
6. Preheat the oven to 180°C.
7. Mix the flour and salt in a bowl making a well in the center. 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. Leave for ten minutes until cool enough to handle.
8. Lightly grease a pie ring measuring 15-20cm by about 8-10cm deep and line the bottom with a disc of lightly greased greaseproof paper. Place it on a similarly lined and greased baking tray.
9. Take two thirds of the dough and, on a lightly floured table, roll it into a circle large enough to line the base and sides of the pie ring and overlap the edge. Place the pastry into the pie ring, carefully pressing into the corners, allowing the pastry to just hang over the edge. Roll the remaining pastry into a circle for the lid.
10. Cover the bottom of the pie with a layer of ham, then a layer of chicken. Repeat this again until the pie is filled. Brush the pie edges with egg wash and place the lid on top.
11. Pinch the lid edge and top pastry edges together with your thumb to crimp the pie and create a seal. Trim the edge with a knife removing any overhanging pastry.
12. Brush the top of the pie with the beaten egg, make a hole in the middle of the pastry lid and cook for 1 hour. Remove the ring and brush the sides and top again with egg before baking for a further 15 minutes. Remove from the oven and leave to cool. Refrigerate for 2-3 hours.
13. When the pie is cold, fill any holes in the pastry with softened butter so that the jelly doesn't escape. Take the jelly from the fridge, remove the layer of fat from the surface and gently reheat to melt the jelly Pour the jelly into the round hole in the top of the pastry until the pie is filled. Return to the fridge until the jelly is set.