Place the beef eye of round in the freezer for 15-20 minutes to firm up, then slice it against the grain into paper-thin pieces.
In a dry pot over medium-high heat, char the onion slices and ginger pieces until they develop dark brown edges and become aromatic.
Add the star anise and cinnamon stick to the pot, toasting for 1 minute until fragrant.
Pour in the beef bone broth and fish sauce; bring to a boil, then reduce heat and simmer for 15 minutes to infuse the flavors.
While the broth simmers, cook the rice noodles according to package directions until tender, then drain and divide into a large bowl.
Strain the broth to remove the solids and return the clear liquid to the pot, keeping it at a rolling boil.
Arrange the raw beef slices over the noodles in the bowl, then pour the boiling broth directly over the meat to cook it instantly.
Top the soup with bean sprouts, cilantro, Thai basil, sliced chili, and a squeeze of fresh lime juice.