Char the aromatics: Place onion and ginger halves cut-side down on a dry skillet over medium heat. Cook until slightly blackened, about 5 minutes per side.

Blanch the bones: Rinse beef bones, then place in large pot with cold water. Bring to boil for 5 minutes, then drain and rinse bones again.

Make the broth: In clean pot, add blanched bones, brisket, charred aromatics, and 5 quarts water. Bring to boil, then reduce to simmer. Skim any impurities.

Toast spices: In dry pan, toast star anise, cinnamon, coriander, fennel, cloves, and cardamom until fragrant, about 3 minutes. Add to broth.

Simmer broth: Add salt, fish sauce, and sugar. Simmer partially covered for 3-4 hours. Remove brisket after 1.5 hours when tender, slice thin.

Prepare noodles: Soak rice noodles in warm water for 30 minutes, then drain. Briefly blanch in boiling water before serving.

Assemble bowls: Place noodles in bowls, top with sliced brisket and raw sirloin. Pour boiling broth over meat to cook it. Garnish with herbs and serve with lime and chili.