Place the halved onion and ginger under a broiler for 5 minutes until charred and fragrant.
In a medium pot, toast the star anise and cinnamon stick over medium heat for 2 minutes.
Add the beef bone broth, fish sauce, charred onion, and ginger to the pot and bring to a simmer.
Cover and simmer the broth for 20 minutes to infuse the flavors, then strain out the solids.
While the broth simmers, cook the rice noodles in boiling water according to package directions and drain.
Slice the raw beef eye of round against the grain into paper-thin pieces.
Divide the cooked noodles into a large bowl and arrange the raw beef slices on top.
Pour the boiling hot broth directly over the beef slices to cook them instantly.
Top with bean sprouts, fresh cilantro, basil, sliced jalapeño, and a squeeze of lime.