Blanch the bones: In a large pot, cover beef bones with cold water, bring to a boil for 5 minutes, then drain and rinse.
Char aromatics: Heat a skillet over high flame. Char onion and ginger (cut-side down) until slightly blackened (~5 mins).
Simmer broth: In a clean pot, add bones, brisket, charred onion, ginger, spices (star anise, cinnamon, cloves, cardamom, coriander, fennel), salt, fish sauce, sugar, and water.
Cook: Bring to a boil, then reduce heat to low. Simmer for 3 hours, skimming foam occasionally.
Strain & slice meat: Remove brisket, strain broth, and discard solids. Slice brisket thinly.
Soak rice noodles in hot water for 15–20 mins until soft, then drain.
Thinly slice raw beef and prepare herbs (basil, cilantro, bean sprouts).
Divide noodles into bowls. Top with sliced raw beef and cooked brisket.
Ladle hot broth over the beef (it will cook the raw slices).
Garnish with herbs, lime, jalapeños, and green onions. Serve with hoisin and Sriracha.