In a large bowl, combine all the ingredients for the marinade. Add the pork, cover with plastic wrap and leave in the fridge to marinate for as long as possible, preferably overnight.
When ready to cook, preheat the oven to 180°C.
Remove the pork from the marinade and reserve marinade. Place the pork in a roasting pan and roast for 40 minutes or until internal temperature reaches 145°F.
While pork is roasting, bring reserved marinade to a boil in a small saucepan. Once the marinade has boiled you can take it off of the heat. Baste pork halfway through cooking with two tablespoons of marinade. Cool remaining marinade to room temperature.
When pork is done, remove from the oven and let rest for 15 minutes, then cut the pork into 1/2cm cubes. Toss the cubed pork in enough of the reserved, cooled, marinade to coat. The pork mixture should be room temperature before filling the pastry.
Preheat oven to 200°C.
Cut each sheet of puff pastry into six 7.5cm squares, for a total of twelve. Brush the edges of each square with beaten egg and then place a heaped teaspoon of the pork filling in the centre. Fold the square in half to create a triangular pastry. Tuck the triangle ends under to round off the triangular shape.
Place on a roasting tray lined with parchment paper and brush egg wash over the top, sprinkle sesame seeds over the top of the pastries and cook in the oven for 18-20 minutes until the pastry is golden. Serve immediately.
**Tip: There is enough marinade for up to 700g pork. Buy a whole pork tenderloin (can’t really buy any less) and cut off the 260g needed for this recipe. Marinate and roast both pieces and use the extra Char Sui to make delicious sandwiches, fried rice, or roast pork salad!