Char the onion and ginger over an open flame or under a broiler until 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, then simmer for 20 minutes.
While the broth simmers, cook the rice noodles according to package directions and drain.
Thinly slice the raw beef eye of round against the grain into paper-thin pieces.
Strain the aromatics from the broth and season with sea salt and black pepper.
Place noodles in a bowl, top with raw beef slices, and pour the boiling broth over the beef to cook it instantly.
Garnish with bean sprouts, Thai basil, jalapeño slices, and a squeeze of fresh lime.