Mix the water, coconut milk, tamarind paste, fish sauce and chicken broth in a large pot (cast iron works best). Add the 2 (or more!) dried chili peppers if desired. Put on high heat, but do not allow to boil.
In the mean time, heat a wok over high heat, add the roasted sesame seed oil and then stir fry the bok choy and bean sprouts over high heat for about 1 minute. You can add a sprinkle of extra fish sauce for extra flavor. Remove from heat and set aside.
Heat the wok over high heat again. Add the beef (or other meat) and cook until almost done. Add directly to the pot with the liquid ingredients.
Check the temperature of the liquid ingredients. Once it is just below boiling, you can add the rice noodles. They will cook VERY quickly! Once they are tender, the soup is ready!
To serve: using kitchen thongs, scoop out the desired amount of beef and rice noodles from the liquid broth. Then, using a ladle, scoop out the desired amount of broth and top with the stir-fried veggies.
Suggested garnish: Lime wedges, basil, scallions, bamboo shoots or lemon-grass.