Halve the onion and ginger; char them in a dry pan over medium-high heat until blackened and fragrant.
In a large pot, toast the star anise and cinnamon stick for 2 minutes, then add the bone broth, charred onion, and ginger.
Simmer the broth gently for 20 minutes, then stir in the fish sauce, coconut aminos, sea salt, and black pepper.
While the broth simmers, prepare the rice noodles according to package directions and drain well.
Slice the flank steak against the grain into paper-thin strips (freezing for 15 minutes beforehand helps with thin slicing).
Divide the noodles into bowls, top with raw beef strips, and pour the boiling hot broth over the meat to cook it instantly.
Garnish with bean sprouts, cilantro, Thai basil, jalapeño slices, and a generous squeeze of lime.