Prepare the pork filling: (recommended to prepare the day or few days before)
If you are cooking on the stove, preheat 1 Tbsp of oil in a heavy-bottom pot. Add the onion, ginger, and garlic and saute for 3 minutes until the onion is soft and fragrant
Add the gochujang paste and pork pieces and stir to mix everything evenly
Add the broth (or water), sugar, soy sauce, and freshly ground black pepper. Scrape the bottom of the pork as you stir everything to make sure nothing catches at the bottom of the pot and get burnt. Make sure all is well-combined
Bring it to a simmer and then lower the heat and cover to let it cook until the pork is tender but doesn't fall apart, about 30 minutes. Test it with a pork. You can easily pierce it but still feel a bit of resistance. We will still bake this later so it will finish cooking in the oven. Proceed to thicken the sauce step below
If using a pressure cooker like Instant Pot, press saute mode and when it says "hot" add 1 Tbsp of oil. Add the onion, ginger, and garlic and saute for 3 minutes until the onion is soft and fragrant. Add the gochujang paste and stir fry another minute
Add pork pieces and stir to mix everything evenly. Add the broth (or water), sugar, soy sauce, and freshly ground black pepper. Scrape the bottom of the pork as you stir everything to make sure nothing catches at the bottom of the pot and get burnt. Make sure all is well-combined
Turn off the saute mode. Close the lid and press "pressure cooker" and make sure it's on "high pressure". Set the timer to 10 minutes. Turn the pressure release valve to "sealing". When it's done cooking, let the pressure release naturally, which may take about 10 minutes or so. Then proceed to thicken the sauce
Thicken the sauce:
There should be some juices released during the cooking process. Scoop out about 5 Tbsp of the liquid from the pot and let it cool down for about 5 minute. Whisk in 3 Tbsp of cornstarch. Carefully pour this into the pork and continue cooking over medium-low heat and keep stirring until the sauce thickens
Remove the pot from the heat and let the pork cool down completely before cooking. Once it has cooled down completely, store it in a container and keep it in the fridge for up to 3 days
For the pie crust: (can be parbaked the day or few days before too)
Follow the instructions in the recipe to partially bake the pie crust and let it cool down completely before using. You can do this the day before. Once the pie crust have cooled down completely, cover with a cling wrap and it can be kept at room temperature until the next day
If you plan to use store-bought, get the one for deep-dish 9-inch pie crust. Follow the instruction for full-baked pie crust and let it cool down completely before using
Assembling:
Preheat the oven to 375 F (190 C) and positioned the oven rack at the lower 3rd of your oven
Transfer the pork filling mixture onto the parbaked crust. It will be thick at this point because it's cold from the fridge if you prepared it the day or few days before. Sprinkle with sesame seeds.
Place the pie plate on a baking sheet lined with parchment paper (to catch dripping if any). Place it on a positioned baking rack and bake for 40-45 minutes or until the sauce is bubbly at the edges
Cool down before cutting:
I did a mistake and cut into the pie too soon, like 10 minutes after it's done cooking and the filling is still a bit "too runny"
I recommend to wait for at least 30 minutes before you cut into the pie. The pie would still be "saucy" and you won't get a clean cut and that's okay. The meat on the top layer has some crisp edges from baking, while the inside of the pie is still tender and juicy