Optional. You can blanch the meat and bones (see notes) to help eliminate blood and any other impurities that might cloud the soup.
In a large pot, combine beef, water, and salt. Turn on the heat and bring to a boil,
When it comes to a boil, skim the scum that rises on the top.
Add onions, green onions (if using), whole peppercorn, and vinegar. Reduce heat to low, cover, and simmer for about 1-2 hours (or 30 minutes if using a pressure cooker) or until beef is tender. Add more water as needed.
Add corn, cover and cook for about 5-7 minutes.
Mix in the potatoes and simmer for about 5 minutes.
Add the beans, cabbage, and fish sauce. Mix well and taste. Season with salt if needed and cook for another 5 minutes.
Put in the pechay, stir and cook for 2 minutes covered and turn off the heat. Let it cook in the residual heat.
Transfer to a serving bowl and serve while hot.
Share and enjoy!