Put water, shanks, and peppercorns (to tenderize meat) in your pressure cooker. Cook for 1 hour on medium heat with the lid affixed.
Once ok to remove the lid, do so and transfer the broth to a stockpot while straining it to remove scum, bones, and peppercorns.
Put the beef shank in the stockpot with broth. Also put in onion, homemade broth and fish sauce. If you don't have homemade broth, use beef bouillion. Simmer to a boil.
If you got the other ingredients like corn, potatoes, and plaintain, put them into the pot. Simmer until the plantains are tender. Skip this step if you don't have them. Put the pak choi and turn off stove.
Season with salt and pepper according to taste.
