1. Roast the beef bones, onion, and ginger at 400°F for 30 minutes.
2. Transfer to a large pot, add water, and bring to a boil. Skim off any foam.
3. Add star anise, cinnamon, coriander seeds, fennel seeds, fish sauce, salt, and sugar. Simmer for 2 hours.
4. Strain the broth and discard the solids.
5. Prepare the rice noodles according to package instructions.
6. Divide the noodles among bowls, top with beef slices, and pour hot broth over to cook the beef.
7. Serve with bean sprouts, fresh herbs, lime wedges, and chili peppers.