Char the onion and ginger over an open flame or under a broiler until blackened and aromatic.
In a large pot, bring the beef bone broth to a simmer with the charred onion, ginger, star anise, and cinnamon stick for 20 minutes.
While the broth simmers, prepare the rice noodles according to package directions, then drain and set aside.
Strain the broth to remove the solids and return the liquid to the pot; stir in the fish sauce, coconut aminos, and sea salt.
Place the cooked noodles in a large bowl and top with the raw, thinly sliced beef eye of round.
Pour the boiling hot broth directly over the beef to cook it instantly until it turns a delicate pink.
Garnish with fresh bean sprouts, Thai basil, sliced chili, and a squeeze of lime before serving.