Prepare the filling (can be a few days before and kept in the fridge):
Preheat a pan with 2 Tbsp of oil. Add red onion and saute for about a minute. Add the water followed by seasonings listed on the ingredient list. Bring it to a simmer. Combine the corn starch with water and mix well. When the water comes to a simmer, gradually pour in the corn starch slurry while the other hand keep stirring with a spatula. When the mixture starts to thicken, add the char siu pieces and keep stirring until all is combined
Remove from the pan to a plate, spread it out to let it cool down completely before using
Prepare the pastry dough:
Prepare the oil dough by combining the flour with the lard in a mixing bowl. Knead with your hand until no more dry flour is visible and it comes into a smooth dough. Cover with a cling wrap while you prepare the water dough
Combine all the ingredients for the water dough in a mixing bowl. Knead until it comes into a smooth dough.
Let both water and oil dough rest for 15 minutes. Take the water dough and flatten it into a disc, bigger than the oil dough. Put the oil dough in the middle. Wrap the water dough around it. Flatten slightly into a disc. Cover it with a cling wrap again and let the dough rest for 15 minutes. This rest is to relax the gluten so you can roll it out easily later
Laminating the dough:
This is how those multiple flaky layers are created, through a laminating process. It sounds more complicated than it actually is.
After resting for 15 minutes, roll the dough out using a rolling pin into a rectangle about 10 x `15 inches, fold the right into 1/3 and the left into 1/3
Rotate 90 degrees and roll it out again into a rectangle. Fold the right into 1/3 again and the left into 1/3
Rotate 90 degrees and roll it out again into a rectangle. This time fold the right to meet with the left in the middle and then fold it over.
Rotate 90 degrees again and roll it out into a rectangle again and use a pizza cutter or dough scraper to cut into 12 roughly equal pieces
At any point during laminating, if you find it hard to roll the dough out, cover the dough and let it rest for 15 minutes and you will have an easier time rolling it out again
Preheat oven to 375 F (190 C) for a conventional oven. For a convection oven, lower the temperature by about 20 degrees. Take one cut-out pastry dough and put about 2 teaspoons of filling in the middle. Fold one side over to cover the filling and then the other. Pinch the two sides to seal tightly. You can use a fork to crimp the edges too
Repeat with the rest of the filling and the dough. Arrange them on a baking sheet lined with parchment paper, about 1 inch apart. Use a sharp knife to make 3 slits on the surface. This is optional
Beat one egg with a fork to loosen the yolk and the white. Add water and beat it again to combine. Use a pastry brush and brush the egg wash on top of the shaped pastry, sprinkle with some sesame seeds
Bake for 25-30 minutes on the middle rack until they are golden brown. Transfer to a cooling rack to let them cool down completely
We found that eating these pastries the next day is even better as the flaky crust is more flavorful
How to reheat in the oven:
Reheat in a preheated oven at 350 F (180 C) for 5-8 minutes or until the pastry is crisp and warm through
How to reheat in the air fryer:
You don't need to preheat your air fryer. Reheat in the air fryer at 350 F (180 C) for 3-4 minutes. You need to monitor carefully as my air fryer may not be the same as yours. You may need a shorter or longer time. Just check every 1-2 minutes to make sure they don't get burnt