1. Slice 2 of the onions into 1/4 inch slices
2. Heat 1 tbs oil in a frying pan and add the sliced onions
3. Cook, stirring, until the outside has browned
4. Remove and drain
5. Slice the remaining onion into paper-thin slices and set aside
6. Rinse the bones and place in a stockpot
7. Cover with cold water and bring slowly to a boil
8. Reduce heat and simmer, uncovered (For a clear broth skim off foam)
9. After 10 - 15 minutes, add browned onion and ginger, carrots, cinnamon, cardamom, star anise, cloves, garlic and peppercorns
10. Bring to a boil
11. Simmer the stock, partially covered for 6 to 12 hours, skimming regularly
12. If necessary add more water to keep the bones covered
13. Strain the stock, skim off, and discard any fat

To Serve:

1. Arrange the sliced beef on a platter
2. Garnish with reserved white and green onion
3. On another platter, arrange the bean sprouts, coriander, chiles and limes
4. Meanwhile, plunge the rice sticks in boiling water to heat and drain
5. Place equal portions in each soup bowl and cover to keep warm
6. Heat beef stock to boiling and season with fish sauce and pepper
7. Pour into a soup tureen or chafing dish
8. At the table, place the soup on a portable warmer to keep hot. Offer each guest a bowl of warm rice noodles
9. Each diner adds some beef and onion to a bowl and Ladle the hot stock over the meat, stirring to cook the meat
10. Add the bean sprouts, coriander, chiles, and lime to taste. Enjoy with chopsticks and a soup spoon