In a large pot, place the beef bones and water. Bring to a boil over high heat, then reduce to medium-low. Skim off any foam that rises to the surface. Simmer for about 30 minutes.
While the broth is simmering, char the halved onion and sliced ginger in a dry skillet over medium heat until they are caramelized and fragrant.
After 30 minutes, add the charred onion and ginger to the pot, along with star anise, coriander seeds, cinnamon stick, cloves, fish sauce, salt, and sugar. Continue to simmer for another 2-3 hours, partially covered.
After simmering, strain the broth through a fine-mesh sieve and return it to the pot. Discard the solids.
Cook the rice noodles according to package instructions, then drain and set aside.
To serve, place a handful of noodles in a bowl, top with a few slices of the raw brisket, and ladle the hot broth over the top.
Serve with fresh basil, bean sprouts, sliced jalapeños, and lime wedges on the side for individual customization.
Notes
Customize with fresh herbs and lime for added flavor.