Char the onion and ginger over an open flame or under a broiler until the skins are blackened and fragrant.
In a large pot, combine the beef bone broth, charred onion, ginger, star anise, and cinnamon stick.
Bring the broth to a boil, then reduce heat and simmer for 20 minutes to allow the spices to infuse.
While the broth simmers, cook the rice noodles according to package directions, then drain and set aside.
Thinly slice the raw eye of round beef against the grain into paper-thin pieces for quick cooking.
Strain the broth through a fine-mesh sieve to remove the solids and return the clear liquid to the pot.
Stir the fish sauce and sea salt into the hot broth, adjusting the seasoning to your preference.
Divide the cooked noodles into a large bowl and arrange the raw beef slices on top in a single layer.
Pour the boiling hot broth directly over the beef slices to cook them instantly until they are just tender.
Garnish the bowl with bean sprouts, fresh cilantro, Thai basil, jalapeño slices, and a squeeze of lime.