Bun dau mam tom, the Hanoi tray with the purple sauce

Bun dau mam tom is the lunch that announces itself from the end of a Hanoi alley. The fried tofu is mild, the noodles are plain, and the small bowl of purple paste in the middle of the tray is the reason the dish exists. Most first-timers smell it before they see it.

What comes on a tray of bun dau mam tom?

A tray of bun dau mam tom arrives on a round, flat bamboo platter lined with a green leaf. On it are squares of fried tofu, blocks of pressed rice noodles cut into pieces, and a handful of herbs and sliced cucumber. Each diner gets a small bowl of mam tom.

The simplest order is tofu and noodles alone. The full tray, called met day du on most menus, adds the pork, the cha com and the spring rolls, and is the one worth ordering the first time.

What is mam tom, and why does it smell that way?

Mam tom is fermented shrimp paste: small shrimp salted and left for months until they break down into a thick purple-grey paste. The smell is powerful and travels across a room, and it is much stronger than the flavour that reaches the mouth once the paste has been prepared.

Preparing it is the diner's job. Squeeze in the kumquat or lime, add a pinch of sugar and some chilli, then stir hard with chopsticks. Many stalls add a spoon of hot oil. The paste lightens in colour and turns foamy, and the foam is the sign it is ready.

The fish sauce guide covers the rest of the fermented family, of which mam tom is the most uncompromising member.

How do you eat bun dau at the table?

Eat bun dau one bite at a time, dipping each piece into the whipped paste. Take a square of tofu with chopsticks, dip it, add a square of noodles and a leaf of perilla or balm, and eat them together. The cucumber is there to reset the palate between bites.

Nobody pours the paste over the tray, and nobody eats the tofu dry. Dip the pork and cha com the same way, and take the spring rolls with either the paste or fish sauce.

You eat bun dau sitting low. Most places serve it at knee-height tables on plastic stools, often in an alley or a courtyard off the street.

Why does the tofu matter so much?

The tofu matters because it is most of the tray, and Hanoi is particular about it. The benchmark is dau Mo, tofu from Mo village, once a separate settlement and now swallowed by the city, where tofu making has been the local trade for generations.

Good bun dau tofu is fried to order, so it arrives crisp and blistered outside and soft enough inside to take the paste. Tofu that arrives lukewarm and leathery left the fryer an hour ago, which is the quickest way to tell a good stall from a tired one.

What does bun dau cost in Hanoi?

A basic tray of tofu and noodles costs about 35,000 to 50,000 dong in Hanoi. A full tray with pork, cha com and spring rolls runs 60,000 to 100,000 dong for one person. At roughly 26,000 dong to the US dollar that is two to four dollars.

Iced tea is usually free or a few thousand dong, and a bottle of beer adds 20,000 or so. The cheap eating guide sets that against the rest of a Hanoi day. Pay in cash with small notes, as the money guide explains.

What if you cannot face the shrimp paste?

Ask for fish sauce instead. "Cho nuoc mam" gets a bowl of diluted fish sauce with garlic and chilli. No stall treats it as an odd request, because plenty of Hanoians order the dish that way.

The tofu, noodles and pork work well with it, and the dish becomes gentler without falling apart. Anyone with a shellfish allergy should skip the paste entirely and say so, since mam tom is made from shrimp and is sometimes stirred with the same chopsticks. The allergies guide covers how to say it.

When do Hanoians eat bun dau?

Hanoians eat bun dau at lunch and through the afternoon, and many stalls open late in the morning and close once the tofu runs out. It is a northern dish, a Hanoi one above all, and the versions sold in Ho Chi Minh City are transplants.

Bun dau sits beside bun cha as one of the two lunches worth planning a Hanoi day around, and the street food guide lists the rest. The alleys around the Old Quarter have more stalls than a week of lunches could get through.