In a pot on medium heat, boil 3 L water. Once boiling, add beef tendons and shanks with 1 tbsp black peppercorns. Let it cook for 45 minutes until tender.
Once tender, add yellow onions and letitcook for 10 minutes.
Add cabbage, potatoes and let it cook for another 10 minutes before adding long beans. Let the long beans cook for 2 to 3 minutes until desired doneness.
Season with 4 tbsp fish sauce and mix well.
Transfer chunks of beef and vegetables into serving bowl. Ladle over soup and serve hot.