Place the beef bones in a large pot and cover with cold water. Bring to a hard boil and boil for 10–12 minutes. Drain the bones, discard the water, and rinse the bones very thoroughly under warm running water. Scrub away any grey foam, blood residue, or loose bits. Wash the pot before continuing. The bones should look clean, pale, and free of grey scum. If you skip this step, your broth will be cloudy and dirty-tasting. That is not rustic; it is just lazy. This aggressive initial boil and rinse forces out the coagulated proteins and impurities that would otherwise cloud the broth during the long simmer to come — removing them now, decisively, protects clarity for the entire remainder of the cook.

Place the onion halves and ginger cut-side down in a dry skillet, under a broiler, or directly over a gas flame. Char until deeply browned and blackened in spots, about 8–12 minutes. Rinse off any loose burnt flakes if needed, but keep the smoky charred aroma. The onion and ginger should smell sweet, smoky, and aromatic. Pale onion and raw ginger give a flat broth. Direct charring caramelises the onion's natural sugars and blooms the ginger's aromatic oils in a way gentle cooking never would — that smoky, sweet character becomes a foundational flavour note running through the entire finished broth.

Return the cleaned bones to the clean pot. Add the brisket or chuck and 4.5 litres cold water. Bring slowly to a gentle simmer. Do not let it boil hard. Skim off any foam that rises during the first 30–45 minutes. Add the charred onion and ginger. Keep the broth at a bare simmer, partially covered, for 1½ to 2 hours, until the brisket is tender. The surface should barely move, with small bubbles rising slowly. If the pot is rolling and boiling, you are wrecking the clarity of the broth. A hard boil physically agitates and emulsifies fat directly into the surrounding liquid, turning a clear broth cloudy in a way that can't be corrected later by straining — the bare simmer specified here is the only way to keep fat and broth as genuinely separate as pho's signature clarity requires.

When the brisket is tender, remove it from the broth and transfer it to a bowl of cold water for 5 minutes to stop the cooking and keep it from drying out. Drain, cover, and refrigerate until slicing. Continue simmering the bones. Do not leave the brisket in the broth for the full bone simmer or it can become dry and stringy. The bones need long cooking; the brisket does not. Shocking the brisket in cold water the moment it's tender halts residual cooking immediately, protecting it from the many additional hours the bones still need — brisket left in that long simmer would simply overcook well past its ideal tender point.

Toast the star anise, cinnamon, cloves, coriander seeds, fennel seeds, and black cardamom if using in a dry skillet over medium heat for 1–2 minutes, just until fragrant. Place the spices in a spice bag, cheesecloth, or fine mesh infuser. Add to the broth during the final 60–75 minutes of simmering. Continue simmering until the broth is aromatic, beefy, and lightly golden. The spices should perfume the broth without dominating it. If you simmer the spices for the full 6 hours, the broth can turn bitter and muddy. This narrow window of exposure is a genuine calibration — the spices need enough time in the hot broth to release their aromatics, but extended contact over many hours would extract harsher, more bitter compounds that a shorter simmer never reaches.

Remove the spice bag, onion, ginger, and bones. Strain the broth through a fine sieve. Season with fish sauce, sugar, and fine sea salt. Taste and adjust carefully. The broth should be savory, lightly sweet, aromatic, and clean. It should taste slightly stronger than a normal soup broth because the noodles and toppings dilute it in the bowl. Good pho broth is not bland beef water. It should have clear beef depth, ginger warmth, sweet onion, spice aroma, and fish sauce salinity without tasting aggressively salty. Seasoning the broth to taste noticeably stronger than a standalone soup is a deliberate adjustment for how it's actually eaten — once poured over noodles, raw beef, and a full plate of garnishes, that same broth will read as properly balanced rather than over-seasoned.

Cook the dried rice noodles according to package directions, usually by soaking first and then briefly boiling, or blanch fresh noodles briefly until hot and loosened. Drain well. The noodles should be flexible and tender but not mushy. Overcooked rice noodles turn the bowl into glue. Rice noodles continue softening from residual heat even after draining, which is part of why they're best pulled slightly before feeling fully done — a noodle that seems perfect straight out of the water can turn soft and gluey by the time it's sitting in a hot bowl of broth.

Slice the chilled cooked brisket thinly across the grain. Slice the raw beef paper-thin. If needed, place the beef in the freezer for 20–30 minutes first so it firms up and slices cleanly. Prepare the white onion, scallions, bean sprouts, Thai basil, lime wedges, and jalapeños. The raw beef must be very thin because it cooks from the heat of the broth in the bowl. Thick slices will stay chewy and awkward. Briefly firming the raw beef in the freezer addresses the same problem that chilling solves for other thin-sliced meats throughout this collection — fully soft, room-temperature beef is too pliable to slice consistently thin, while a firm, partially chilled piece holds its shape cleanly under the knife.

Warm 4 large bowls. Divide the hot noodles among the bowls. Add sliced cooked brisket. Lay the raw beef slices over the noodles in a single layer. Add thin white onion and scallions. Bring the broth back to a full boil. Ladle the boiling broth directly over the raw beef to cook it lightly. Serve immediately with bean sprouts, Thai basil, lime wedges, jalapeño slices, and extra herbs on the side or arranged at the bowl edge. The broth must be boiling hot when it hits the beef. The beef should turn from raw red to pink and tender in the bowl, not grey and overcooked. Genuinely boiling broth is what cooks the paper-thin raw beef gently and evenly the instant it's poured — broth that's merely hot rather than actively boiling won't carry enough heat to properly cook that beef through in the brief window before serving.