Char halved onion and sliced ginger in a dry pan over medium-high heat until fragrant and blackened in spots.
In a large pot, toast star anise and cinnamon stick for 1 minute, then add beef bone broth, charred onion, ginger, and fish sauce.
Simmer the broth gently for 20 minutes to allow the spices to infuse, then strain through a fine-mesh sieve.
Cook rice noodles in a separate pot according to package instructions, drain, and place in a large serving bowl.
Arrange the raw, thinly sliced beef eye of round in a single layer over the cooked noodles.
Bring the strained broth back to a rolling boil and pour it immediately over the beef to cook it until tender.
Garnish the bowl with bean sprouts, cilantro, Thai basil, sliced jalapeño, and a squeeze of fresh lime.