Char the onion and ginger under a broiler for 5 minutes until the skins are blackened and fragrant.
In a large pot, toast the star anise and cinnamon stick over medium heat for 2 minutes until 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 extract the spice flavors, then strain through a fine-mesh sieve into a clean pot.
While the broth simmers, cook the rice noodles in a separate pot of boiling water according to package instructions, then drain.
Place the cooked noodles into a large serving bowl and top with the raw, paper-thin slices of eye of round beef.
Ladle the boiling hot broth directly over the beef to cook it through and garnish with bean sprouts, Thai basil, jalapeño, and lime.