Bun thang is one of those dishes that Hanoians consider a marker of local identity precisely because it's not well known outside the city. The broth is light and clear, made from chicken and dried shrimp, delicate where pho is assertive. Into it go fine rice vermicelli noodles, shredded chicken, thin-sliced Vietnamese ham, and a web of egg crepe strips cut into threads. On the side comes a small pot of mam tom — fermented shrimp paste, pungent and purple — which you add to taste. The combination is subtle, complex, and completely unlike anything else in Vietnamese cooking.
Ba Duc is one of the long-standing specialists in bun thang in the Old Quarter, a counter operation that has been serving it to the same neighborhood for decades. The bowls are smaller than pho, the portions considered adequate rather than generous. Order the bun thang and add your own mam tom — don't skip it, even if fermented shrimp paste sounds alarming; without it, the bowl is incomplete. Most foreign visitors to Hanoi eat pho for breakfast every day and never encounter bun thang; this is the correction.