Preheat the oven to 180 ºC.
Place the pork shoulder into a deep oven tray. Mix the garlic, thyme, salt, pepper, nutmeg and olive oil in a small bowl. Rub this spice mixture all over the pork and pour the chicken stock into the tray. Cover the tray with foil and place into the oven. Roast the pork for 3 hours until pulled apart tender.
When the pork is roasted, remove it from the oven, pour the juices into a jug, and reserve. Use two forks to shred the pork.
Heat a medium-sized saucepan and add the olive oil. Add the chopped mushrooms and fry until browned and caramelised. Deglaze the pan with the brandy and cook for 1 minute. Add the roasting juices to the mushrooms and bring to a boil, then reduce to a simmer and add the cream. Add the Parmesan cheese and simmer for about 3 minutes, then add the shredded pork and heat through. Taste and adjust the seasoning with salt and pepper.
Line a baking tray with baking paper.
Unroll one roll of pastry and leave it on the plastic it was rolled in. Using the 4 cm cookie cutter, cut out 25 circles (or as many as it yields), then place these pastry circles upside down on the prepared baking sheet.
Beat the egg yolk and milk together and then brush the circles with this mixture – take care not to brush too close to or around the sides of the circles, as this can cause the pastry not to rise properly.
Unroll the second sheet of pastry and keep it on the plastic it was rolled in; cut the same amount of circles using the same size cutter as previously. Then, take the smaller cookie cutter and cut out the centres of these circles. You will end up with a doughnut-shaped ring of pastry; lift these, turn them upside down and place them on top of the original circles that you have already egg washed. This will form the sides of your vol-au-vent as it cooks and rises. You will now have 25 circles of pastry – one full circle topped with a ring-shaped piece of pastry.
Using a fork, prick the bottom pastry in the centre hole of the ring layer to prevent it from puffing up during baking. Brush the top of the ring circles with egg wash, but again, be careful not to get it on the sides; otherwise, your vol-au-vents may not rise properly.
Note: the circles that were removed from the centre of the pastry rings, as well as any leftover pastry, can be egg washed and cooked separately. The round centre pieces can serve as ‘hats’ for the vol au vents, should you choose to use them.
Place the tray into the oven for 15 to 20 minutes, or until the vol-au-vents are well-risen and golden. Remove the pastry cases from the oven and allow them to cool.
Turn the oven to the grill setting. Lay the bacon on a baking sheet and place it into the oven for 8-10 minutes to cook until crispy. Alternatively, cook in an air fryer. Let it cool slightly, then chop to a fine crumb.
Add 1-2 teaspoons of the pork and mushroom mixture to each vol-au-vent to fill. Sprinkle bacon crumbs over the top of each vol au vent and garnish with chopped chives. Serve immediately.