Char the onion and ginger in a dry pan over high heat until blackened in spots to release deep, smoky flavors.
In a medium pot, toast the star anise and cinnamon stick over medium heat for 1-2 minutes until highly aromatic.
Pour in the beef bone broth and add the charred onion, ginger, fish sauce, sea salt, and black pepper.
Simmer the broth gently for 20 minutes to infuse the spices, then strain out the solids and return the liquid to a boil.
While broth simmers, cook the rice stick noodles according to package directions, drain, and place in a large serving bowl.
Thinly slice the raw beef eye of round against the grain into paper-thin pieces.
Arrange the raw beef slices on top of the cooked noodles in the bowl.
Pour the boiling hot broth directly over the beef to cook it instantly, then garnish with bean sprouts, basil, cilantro, scallions, and a squeeze of lime.