Char the halved onion and sliced ginger in a dry pot over medium-high heat until fragrant and slightly blackened.
Add the beef bone broth, star anise, and cinnamon stick to the pot and bring to a gentle simmer for 15 minutes.
While the broth simmers, cook the rice noodles according to package directions, then drain and set aside.
Strain the aromatics from the broth and stir in the fish sauce, sea salt, and black pepper.
Divide the cooked noodles into a large bowl and top with the raw, thinly sliced beef.
Pour the boiling hot broth over the beef to cook it instantly to a tender medium-rare.
Garnish with bean sprouts, Thai basil, cilantro, jalapeño slices, and a squeeze of lime.