This pie looks difficult but needs only about 45 minutes of active work – much of the time it takes to make is taken up with letting the dough rest in the fridge to firm up. Commercial puff pastry sheets vary in size and weight, so adapt the size (and shape) of the pie according to the brand of pastry you buy.
The all-butter puff pastry I use (Waitrose) comes as two sheets that are about 28cm x 22cm (11 x 8½ in), so the brand you use should give you about the same total area of pastry. This recipe makes two pies that are about 12cm by 18cm (5 x 7 in), which I like because making two pies gives you a better crust-to-filling ratio than if you were to make one large square or round pie. You can make it as one large pie, of course, but you will need to bake it for longer.
If possible, buy cooked chestnuts from the roasted chestnut vendor, because they have a deliciously smoky flavour. Remove the shells and papery skin while the chestnuts are hot. You can also use cooked, plain (unsweetened) shelled chestnuts, sold in foil packs, or you can roast fresh chestnuts in the oven.
Keep all the ingredients cold, especially the puff pastry. Be sure to defrost the puff pastry in the fridge; if you do it at room temperature, the dough will sweat too much.
Put the pork in a bowl and add the soy sauce, rice wine, salt, sugar, pepper, cornstarch and sesame oil. Mix well, then refrigerate while preparing the other ingredients.
Cut the shimeji mushrooms into 2.5cm (1 in) lengths. Cut the chestnuts into large dice. Mince the shallots. Halve the garlic cloves, then thinly slice them.
Slice the Chinese bacon as thinly as possible. Quarter the Chinese sausage lengthwise, then cut it into medium dice.
Heat a wok or skillet over a medium flame – no need to add oil. Add the bacon and sausage to the pan and cook, stirring often, until the meats are cooked through and slightly browned in spots. Remove the meats from the pan, leaving behind as much fat as possible, and drain on paper towels.
Pour off all but about 15ml (1 tbsp) of the fat from the wok or skillet (no need to wash it). Place the pan over a medium flame. When the fat is hot, add the shallot and garlic and stir-fry for about 30 seconds, or until slightly softened.
Add the mushrooms and chestnuts to the pan and stir-fry until the mushrooms start to soften (about 45 seconds). Transfer the ingredients to a bowl and leave to cool.
When the Chinese meats, the mushrooms and chestnuts are cool enough, add them and the black pepper to the bowl with the minced pork, then mix well. Refrigerate the mixture.
Working with one sheet of puff pastry at a time (keep the other refrigerated), cut it in two pieces, one about 4cm (1½ in) wider than the other. Lay the pieces on a parchment-paper-lined baking tray. Do the same for the second sheet of puff pastry.
Divide the filling between the two smaller pieces of puff pastry, leaving a 1.5cm (⅔ in) border along each long edge, and a 4cm (1½ in) border on the short edges. Press the filling to compact it, then smooth the surface. Refrigerate for about 15 minutes, or until the dough is firm.
Whisk the egg, then use it to lightly brush the edges of the two smaller sheets of puff pastry. Carefully lift the larger pieces of puff pastry over the smaller pieces, trying not to stretch them. Press the top layer over the bottom so the edges adhere. Use the sides of your hands to press the edges together so each pie is sealed firmly on all four sides and the filling is enclosed tightly. Refrigerate for about 15 minutes, or until the dough is firm.
Use a pizza wheel or a knife to trim the edges of each pie, leaving a 1cm border along all four sides. Save the trimmings. Refrigerate the pies and the trimmings for about 15 minutes.
Keep the pies in the fridge. Thinly roll out the trimmings, then use a 2.5cm (1 in) round fluted cutter to cut six circles of dough. Use a small round cutter (or a metal straw) to cut a small hole in the centre of each dough circle. Use other small decorative cutters (such as stars) to cut whatever small shapes you like from the remaining dough. Refrigerate all the shapes.
Take the pies from the fridge. Use your fingertips to flute the edges along all four sides of each pie, pressing firmly so the edges are sealed tightly. Use a small round cutter (or metal straw) to cut three air vents in the top of each pie, placing them at even intervals. Lightly but evenly brush the pies with egg, then refrigerate for at least 15 minutes, or until firm.
Place the dough circles over the three air vents on each pie, making sure the small holes align. Place the other decorative shapes on the pie. Lightly but evenly brush the pies with the egg. Refrigerate the pies for at least 15 minutes.
Preheat the oven to 225 degrees Celsius (440 degrees Fahrenheit). Bake the pies for 15 minutes, then turn the heat to 180 degrees Celsius (360 degrees Fahrenheit). Turn the pies around in the oven and bake for 10 minutes, or until fully cooked. When ready, the pastry will be glossy and medium brown, and when you carefully lift the pies with a wide metal spatula, the bottoms will be well browned. If the edges get too dark before the pies are fully baked, cover them with strips of aluminium foil.
Cool the pies for at least 15 minutes. Serve warm or at room temperature. Serves four as a main course, or eight to 12 as a starter.