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

Prepare the broth: In a large pot, add beef bones and brisket. Cover with water and bring to a boil. Skim off any foam, then reduce heat to a simmer.

Toast the spices: In a dry pan, toast star anise, cinnamon, cloves, cardamom, and coriander seeds until fragrant, about 2-3 minutes. Add to the broth along with charred onion and ginger.

Simmer the broth: Add salt, sugar, and fish sauce. Simmer uncovered for 3 hours, occasionally skimming fat and impurities. Remove brisket after 1.5 hours, slice thinly when cool.

Prepare noodles: Soak rice noodles in warm water for 20 minutes, then drain. Cook in boiling water for 30 seconds, then divide among serving bowls.

Assemble pho: Top noodles with sliced brisket and raw sirloin. Ladle hot broth over meat (it will cook the sirloin). Garnish with bean sprouts, herbs, lime, green onions, and chilies.

Serve immediately with hoisin sauce and Sriracha on the side for dipping and adjusting flavor.