Bún Bò Huế Broth

Place the beef shin and pork trotters in a large pot and cover with cold water. Bring to a vigorous boil over high heat — this first boil is not for making broth, it is for purging. After 5–7 minutes at a full boil, a grey, foamy scum will have risen to the surface. Drain and discard the blanching water entirely. Rinse each bone under cold running water, scrubbing away any grey residue, blood clots, and bone fragments with your fingers. This parboiling step is non-negotiable for a clear, clean-tasting Huế broth — it removes blood, myoglobin, and impurities that would otherwise cloud the stock and give it a strong liver-like smell.

Place the blanched bones in a large stockpot with the 3 liters of cold water, lemongrass pieces, and charred shallot halves. Charring the shallots over an open flame or under a broiler until the cut surface is blackened adds a complex smoky-sweet note that is characteristic of Vietnamese stocks. Bring to a simmer over medium-high heat. As soon as you see the first wisps of steam, reduce heat to maintain a very gentle simmer — the surface should merely tremble, with a bubble breaking through every 2–3 seconds. Add the salt. Skim any foam that rises in the first 20 minutes. Then leave to simmer, mostly undisturbed, for 3–4 hours until the broth is deeply savory and the pork bones have given up their collagen. The broth should have a faint golden clarity.

In a small saucepan, heat the neutral oil over medium heat until shimmering. Add the annatto seeds and stir — they will immediately begin to leach their vivid orange-red pigment into the oil. Cook for 2–3 minutes until the oil has turned a deep, clear orange-red. Strain out and discard the annatto seeds. Return the colored oil to the pan and add the minced garlic, cooking until golden and fragrant (about 1 minute). Add the chili flakes and stir for 30 seconds. Add the fermented shrimp paste and fry it in the spiced oil for 1–2 minutes, breaking it up and letting it caramelize slightly — this frying step tames its raw, ammonia-forward edge and deepens it into something complex and savory. The paste will smell aggressively funky at first, then mellow into a deeper, almost seafood umami.

Pour the annatto-chili oil compound into the strained broth. Add the fish sauce. Stir thoroughly and bring to a simmer. Now add the remaining fermented shrimp paste, dissolving it directly into the simmering broth a little at a time — taste after each addition. The shrimp paste carries enormous saltiness and funk, so add it slowly. The finished broth should be deeply savory, quite salty, lemongrass-scented, and carry a slow-building heat. It should look a vivid amber-orange from the annatto. Adjust with more fish sauce for salt, more chili oil for heat. The broth is used to assemble bún bò Huế: thick round rice noodles, sliced beef and pork, pork blood cubes, and abundant herbs.