Char the onion and ginger over an open flame or in a dry pan until fragrant and slightly blackened.
In a medium pot, combine the beef bone broth, charred onion, ginger, star anise, and cinnamon stick.
Bring to a boil, then reduce heat and simmer for 15 minutes to infuse the flavors.
While broth simmers, cook the rice noodles according to package directions until tender, then drain and set aside.
Strain the broth to remove the solids and return the liquid to the pot, seasoning with fish sauce, sea salt, and black pepper.
Place the cooked noodles in a large bowl and top with the raw, thinly sliced beef.
Pour the boiling hot broth over the beef to cook it instantly until it reaches a tender, pink finish.
Garnish with bean sprouts, cilantro, and Thai basil before serving.