Place the halved onion and sliced ginger face down in a dry pan over medium-high heat until charred and fragrant.
In a medium pot, toast the star anise and cinnamon stick for 1 minute, then add the beef bone broth, charred onion, ginger, fish sauce, sea salt, and black pepper.
Bring the broth to a boil, then reduce heat and simmer for 20 minutes to allow the flavors to meld.
While the broth simmers, cook the rice noodles according to package instructions, drain, and set aside.
Freeze the beef eye of round for 15 minutes to make it easier to slice, then cut it into paper-thin strips against the grain.
Strain the broth to remove the solids and return the clear liquid to the pot on a rolling boil.
Place the cooked noodles in a large bowl and lay the raw beef slices on top.
Pour the boiling broth over the beef to cook it instantly, then garnish with bean sprouts, cilantro, Thai basil, jalapeño slices, and a squeeze of lime.