Preheat a large skillet with cooking oil. Add in the onion and cook until they are soft and fragrant, about 5 minutes. Add in the
Let the puff pastry sit at room temperature (if frozen) until you can easily fold the pastry, but not to the point of too soft and sticky. Add in the char siu and continue to stir fry for another 1 minutes. Add in hoisin sauce, brown sugar and continue to stir until combine. Add in water and bring to a boil and then add flour and continue to stir until the mixture is thickened. Have a taste. It should be sweet and savory. Add more brown sugar and salt as needed. Remove from heat and let it cool down completely before wrapping
Let the puff pastry sit at room temperature for few minutes until you can easily fold it (but to the point of too soft and sticky).
Dust your work surface with some all-purpose flour. Roll the pastry out until it is about 1/4-inch thickness. Use a pastry cutter if you have one to cut it out into about 2-inch square
Preheat the oven to 375 F. Place about 1 tsp or more of filling in the middle of the square and then cover with another square. Pinch the edge to seal and use a fork to make some imprints (as shown in the video). Repeat with the rest. Place them in a baking sheet lined with parchment paper
Brush each pastry with beaten egg and sprinkle with some white sesame seeds and bake for about 15-20 minutes (depending on the oven) until they are golden brown. Served warm
Chinese roast pork puff pastry https://whattocooktoday.com/chinese-roast-pork-puff-pastry.html