In a large pot, add the beef bones and cover with water. Bring to a boil over high heat.
Reduce heat to low and simmer for at least 2-3 hours to extract flavor. Skim off any foam or impurities that rise to the surface.
Add lemongrass, shallots, garlic, shrimp paste, fish sauce, and annatto seeds to the pot. Continue simmering for another hour.