
Char the aromatics first. Heat a heavy skillet over high heat until very hot, then place the halved onions and ginger cut-side down in the dry pan. Cook until well charred on both sides, then set aside.
In the same dry skillet, toast the star anise, cinnamon quills, cardamom pods, and coriander seeds over medium-high heat for about 3 minutes, shaking the pan often, until fragrant.
To clean the broth, place the beef brisket, meaty beef bones, and marrow bones in a large stockpot and cover with water. Bring to a boil and cook for 5 minutes to release impurities.
Drain the pot completely, then rinse the brisket and bones well under running water. Wash out the pot to remove any residue before starting the broth.
Return the cleaned bones and brisket to the pot. Add 3.5 liters water, the charred onions and ginger, toasted spices, sugar, and salt. The liquid should just cover the ingredients.
Bring the pot to a gentle boil, then immediately lower the heat to a steady simmer. Cover with a lid and simmer for 3 hours, skimming the surface occasionally if needed.
Remove the brisket once it is tender enough to slice easily. Let it cool, then refrigerate until ready to serve.
Continue simmering the broth uncovered for 40 minutes to concentrate the flavor. Strain the broth into a clean pot and discard the bones and spices.
Stir the fish sauce into the strained broth. Taste and adjust with a little more salt or sugar if needed; the broth should taste rich, savory, lightly sweet, and aromatic.
Cook the rice noodles according to the package directions just before serving, then drain well. Slice the chilled brisket thinly.
Divide the cooked noodles among serving bowls. Top each bowl with sliced brisket and a few slices of raw beef tenderloin.
Ladle very hot broth over the beef so the tenderloin cooks gently in the bowl. Serve immediately with bean sprouts, Thai basil, cilantro, lime wedges, sliced red chili, hoisin sauce, and sriracha on the side.
