Char the onion and ginger over an open flame or under a broiler until slightly blackened and fragrant.
In a large pot, toast the star anise and cinnamon stick over medium heat for 2 minutes to release their oils.
Add the beef bone broth, charred onion, ginger, and fish sauce to the pot and simmer gently for 20 minutes.
While the broth simmers, cook the rice noodles according to package directions, drain, and set aside in a serving bowl.
Thinly slice the raw beef eye of round against the grain into paper-thin pieces to ensure they cook quickly in the broth.
Strain the broth to remove the solids and return the clear liquid to the pot, bringing it to a rolling boil.
Arrange the raw beef slices over the cooked noodles in the bowl.
Ladle the boiling broth over the beef to cook it instantly, then garnish with bean sprouts, basil, jalapeño, and a squeeze of lime.