Char the onion and ginger over an open flame or under a broiler until blackened and fragrant to unlock deep aromatics.
In a large pot, toast the star anise and cinnamon stick for 1-2 minutes until fragrant, then add the beef bone broth, charred onion, ginger, and fish sauce.
Bring the broth to a boil, then reduce heat and simmer for at least 20 minutes to develop the complex, savory flavors.
While the broth simmers, cook the rice stick noodles according to package directions, drain, and set aside in a serving bowl.
Thinly slice the raw beef sirloin against the grain into paper-thin pieces for maximum tenderness.
Strain the broth to remove the solids and return the clear liquid to the pot, seasoning with sea salt and black pepper.
Arrange the raw beef slices over the cooked noodles and pour the boiling hot broth directly over the beef to cook it instantly.
Garnish the bowl with fresh bean sprouts, Thai basil, cilantro, jalapeno slices, and a generous squeeze of lime.