Trim any large pieces of fat from the pork shoulder, then cut it into 3-4 substantial chunks. You want pieces big enough that they won't fall apart during searing but small enough to fit comfortably in your pressure cooker.
Get your cast iron pan screaming hot over medium-high heat, then add the oil. Sear each pork chunk until you get a deep golden crust on all sides — this takes patience, about 3-4 minutes per side. The browning creates the flavor foundation for everything that follows.
Transfer the seared pork to your Instant Pot along with the quartered onion, minced garlic, 1 teaspoon of the salt, all the pepper, and the chicken stock. The liquid should come about halfway up the meat — that's perfect for pressure cooking.
Lock the lid in place and make sure the steam vent is set to sealing. Select pressure cook on high for 60 minutes. The cooker will take about 10-15 minutes to come to pressure, then the actual cooking begins.
⏱ 1 hr
Once the timer goes off, resist the urge to quick-release. Let the pressure come down naturally for 10-20 minutes — this gentle cooldown keeps the meat incredibly tender. You'll hear the float valve drop when it's ready.
⏱ 20 min
Carefully remove the pork with a slotted spoon and set it aside. Pour the cooking liquid through a fine-mesh strainer into a bowl, then skim off any surface fat with a spoon. Discard the solids and return the strained liquid to the pot.
Shred the pork with two forks — it should pull apart effortlessly. Return the shredded meat to the pot with the cooking liquid, add the remaining teaspoon of salt, and hit the sauté button. Cook just until everything is heated through and the flavors meld, about 3-4 minutes.