For the filling, pulse 200g/7oz of the pork and all of the bacon in a food processor until it resembles mince.
Tip the mixture into a bowl and add the remaining filling ingredients, including the remaining roast pork. Stir until well combined.
For the pastry, sift the flour into a bowl.
Heat the milk, lard and water in a saucepan until the lard has melted. Stir until well combined.
Stir the hot milk mixture into the flour until the mixture comes together as a dough.
Roll the pastry out thinly onto a lightly floured work surface and use it to line 4-6 small pie moulds. (Alternatively, you could use the wells of a muffin tin.)
Divide the pork filling mixture among the pie moulds and bake in the oven for 45-50 minutes, or until the filling is cooked through.
Meanwhile, for the balsamic onions, heat the oil in a frying pan over a medium heat and fry the onions for 2-3 minutes, or until softened.
Add the sugar and vinegar, bring the mixture to the boil and cook for 8-10 minutes, or until the onions are sticky.
Remove the pies from the oven and allow to cool slightly. Carefully remove the pies from the moulds, brush the sides with the beaten egg yolk and place onto a baking tray.
Spoon the balsamic onions on top of the pies and sprinkle over the cheese.
Bake the pies in the oven for a further 5-6 minutes, or until the cheese is bubbling and golden-brown.
