Bún Riêu Cua (Rice Noodles in a Crab Broth with Crab Curds)

Variations

• Bún riêu tôm: the same family made with prawns instead of crab. The prawns are usually minced and bound with egg before they go in.
• Bún riêu ốc: with paddy snails, boiled and laid on top of the crab riêu.
• Southern style: crab meat mixed with minced pork and egg into one mass and spooned into the broth. It is a shaped dumpling rather than a raft that forms by itself, so steps 3 and 4 here do not apply.
• With blood: Hanoi shops often add cubes of set pig's blood.
• Beside sinigang: the Philippine soup soured with tamarind. There the solids are meat and vegetables; here the solid part forms out of the broth itself.

Tips

• This is the technique for clearing a broth, except that what gets skimmed off is dinner. Ukha clarifies with an egg white: "the white sets around whatever is suspended and rises. Skim it off." What it skims is discarded. In bún riêu cua the crab's own protein does the egg white's job, and what rises is the solid part of the bowl. Which is why the crab liquid left underneath after step 5 is far clearer than the grey liquid you strained.
• How it becomes curds is already written on egusi soup. Egusi: "Its protein coagulates with heat, so instead of dissolving it sets into soft curds", and the way to keep them is the same too — "leave it alone for ten minutes without stirring". The difference is what goes in. Egusi goes in as lumps of paste; the crab goes in pounded, strained and liquid. Nobody shapes the curds: protein dissolved in the water sets with heat and gathers by itself. That is why step 4 stops stirring once the pan steams — stirred while it is gathering, it scatters into cloudiness instead.
• A hard boil fails for the same reason. As ukha says, "boiling only clouds it". In this pot the cost is higher: the broth clouds, and the thing that was going to be the solids breaks up and is gone.
• Why pound the shells. Paddy crabs are too small to pick. Pounding and working them in water moves the meat and its protein into the liquid, and the shell stays in the sieve. The second straining is there to wash out what meat is left.
• The egg is insurance. Crab alone will gather, but an egg makes the mass firmer and less likely to break when you ladle it in step 5. It dilutes the crab flavour a little.
• The sourness is split between tomato and tamarind. Fried tomato gives sweetness and colour, tamarind the sourness underneath. Mắm tôm goes into the pot by the spoonful only; the rest is added at the table, bowl by bowl.
• Cook the noodles separately. Boiled in the broth, rice noodles shed surface starch and cloud a broth that has only just been cleared.