Char the halved onion and ginger piece over an open gas flame or under a high broiler until the surfaces are blackened and fragrant.
In a large heavy-bottomed pot, toast the star anise and cinnamon stick over medium heat for 1 minute until their oils are released.
Add the beef bone broth, charred onion, charred ginger, and fish sauce to the pot and bring to a gentle boil.
Reduce the heat and simmer the broth for 20 minutes to allow the aromatics to infuse, then season with sea salt and black pepper.
While the broth simmers, cook the rice stick noodles in a separate pot of boiling water according to package directions, drain, and divide into serving bowls.
Thinly slice the raw top round beef against the grain into paper-thin pieces using a very sharp knife.
Arrange the raw beef slices in a single layer over the cooked noodles in each bowl.
Pour the boiling hot broth through a mesh strainer directly over the beef slices to cook them instantly and fill the bowl.
Top the pho with fresh bean sprouts, cilantro, basil, and jalapeño slices, serving with lime wedges on the side.