In a large pot, combine beef shanks and enough cold water to cover. Bring to a boil.
Drain beef and rinse under cold water to remove impurities. Discard the liquid and rinse the pot.
In the pot, return meat and enough cold water to cover. Bring to a boil, skimming scum that accumulates on top.
When the broth has cleared, add onions, garlic, peppercorns, and fish sauce.
Lower heat to low, cover, nd cook at a bare simmer for about 3 hours or until meat is fork-tender. Season with salt to taste.
In a medium pot over medium heat, bring about 2 cups water to a boil. Add cabbage and cook for about 1 to 2 minutes or until tender yet crisp.
With a slotted spoon, remove from heat and immediately plunge into a bowl of iced water. Let cool completely and drain well.
In another pot over medium heat, bring about 2 cups water to a boil. Add egg noodles and cook for about 10 to 15 seconds. Remove from water and rinse with cold water. Drain well.
Divide egg noodles into serving bowls. Add beef shanks and cabbage. Pour hot broth. Garnish with fried garlic bits and chopped onions. Serve hot.