Pour water and beef broth in a soup pot. Let boil
Add the whole peppercorn and onion. Boil for 5 minutes.
Put the beef shoulder bones in the pot. Cover and then let the liquid return to a boil. Adjust the heat between low to medium. Cook for 60 to 120 minutes.
Once the tendons are tender (this has a tendency to slip-off the bones), add the potato and cabbage. Cook for 5 minutes.
Add the fish sauce. Adjust the taste by adding more if needed. Cook for 5 more minutes.
Transfer to a serving bowl. Serve with a saucer of spicy fish sauce with lemon and a cup of rice on the side.
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