- To prepare the stock: Blanch the beef bones briefly in boiling hot water. Rinse and place in a stock pot with the rest of the ingredients. Bring to a boil and skim off surface scum from the stock.
- Reduce the heat, cover and simmer for 1½-2 hours. Skim off any scum that appears, then strain the stock through a fine sieve. Put the stock over a very low heat to keep it warm.
- To serve: In another pot, bring water to a boil and add the dried noodles. Cook until noodles are tender but not mushy. Beansprouts can be scalded briefly or, if preferred, kept crunchy.
- Put a little of the prepared noodles in each serving bowl and add a few slices of beef tenderloin. Pour the hot soup stock over.
- Put some beansprouts, basil leaves, coriander leaves and a slice of lime on a separate plate. Serve immediately with chillies and spring onion.
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