Place the onion and ginger over an open flame or under a broiler until charred and fragrant.
In a medium pot, toast the star anise and cinnamon stick over medium heat for 2 minutes until aromatic.
Add the beef bone broth, charred onion, ginger, and fish sauce to the pot and simmer for 20 minutes.
While the broth simmers, cook the rice noodles according to package directions, then drain and place in a large bowl.
Thinly slice the raw beef eye of round against the grain into paper-thin pieces.
Strain the broth through a fine-mesh sieve to remove the solids and return the liquid to a rolling boil.
Arrange the raw beef slices in a single layer over the cooked noodles in the bowl.
Pour the boiling hot broth directly over the beef to cook it instantly and season with black pepper.
Garnish the soup with bean sprouts, cilantro, Thai basil, and a fresh squeeze of lime before serving.