Roast beef bones, onion, and ginger until browned
Rinse the bones well
Simmer bones in a large pot with water
Skim off foam and impurities
Add charred onion, ginger, star anise, cinnamon, cloves, coriander seeds, and fennel seeds
Simmer gently for several hours
Add fish sauce, salt, and a little sugar to taste
Strain the broth
Cook rice noodles according to package instructions
Slice raw beef thinly
Prepare toppings such as bean sprouts, Thai basil, cilantro, lime, jalapeño, and scallions
Place noodles in bowls
Add raw beef on top
Ladle hot broth over the beef
Serve with toppings and condiments