Place the halved onion and ginger cut-side down in a dry pan over medium-high heat until charred and fragrant.
In a large pot, toast the star anise and cinnamon stick for 1 minute, then add the charred onion, ginger, and beef bone broth.
Bring the broth to a boil, then reduce heat and simmer for 20 minutes before stirring in the fish sauce.
While the broth simmers, cook the rice noodles according to package directions and drain.
Thinly slice the raw beef eye of round against the grain into paper-thin pieces.
Divide the noodles into a large bowl, top with the raw beef slices, and pour the boiling hot broth over the beef to cook it instantly.
Garnish with bean sprouts, Thai basil, cilantro, jalapeno slices, and a squeeze of fresh lime juice.