The central Vietnamese city of Hue, once the capital of Vietnam and still known as the Imperial City, has a distinctive cuisine full of diminutive rolls, savory pancakes, dumplings, skewers and other snacky bites.

Standing in contrast is the mighty Bun Bo Hue, a soup that starts with pork and beef bones, gets a kick from lemongrass, annatto and shrimp paste, and finishes the job with a tangle of herbs, a squeeze of lime and a few delicious add-ons like sliced brisket, crab balls and, in some cases, cubes of congealed pig’s blood.

Phew! As with a ragu Bolognese, most cooks can agree on the basic structure of the dish, but everyone makes it with slight variations — and there’s no end ...