Bún riêu: crab noodle soup

Bún riêu is a Vietnamese noodle soup made with a tangy tomato broth, rice vermicelli and riêu, soft clusters of crab that float to the top like curds. It's lighter and brighter than phở, with a gentle sourness from tomatoes and savory depth from crab and shrimp paste.

What is riêu?

Traditionally, riêu is made from small freshwater paddy crabs (cua đồng). Cooks pound the whole crabs, strain the liquid and heat it slowly. As the broth warms, the crab proteins rise and set into soft, fluffy rafts. That's the signature look of the dish.

Outside Vietnam, paddy crabs are hard to find. Many home cooks use jarred crab paste in soybean oil, sold in Asian grocery stores, mixed with ground pork and eggs. The egg binds everything so it still forms curds.

North vs South

• Northern (Hà Nội) style tends to be simpler: crab, tomato, a clean broth and herbs, sometimes with fried tofu.
• Southern style usually piles on more toppings, such as pork, fried tofu and sometimes blood cubes, plus a red-orange oil made from annatto seeds.

Both come with a plate of herbs and vegetables and a spoonful of mắm tôm (fermented shrimp paste) on the side for those who like it.

Ingredients (serves 4)

For the broth:

• 2 lb (about 900 g) pork bones, or 8 cups (2 liters) low-sodium chicken or pork stock
• 2 tablespoons dried shrimp, rinsed (optional)
• 4 ripe tomatoes, cut into wedges
• 3 shallots, sliced
• 2 tablespoons fish sauce, plus more to taste
• 1 teaspoon sugar
• 1 tablespoon tamarind paste or a squeeze of lime, for sourness

For the crab curds:

• 1 jar (about 6 oz / 170 g) crab paste in soybean oil
• 8 oz (225 g) ground pork
• 3 eggs
• 1 tablespoon fish sauce
• ½ teaspoon black pepper

To serve:

• 1 lb (450 g) thin rice vermicelli (bún), cooked and rinsed
• 8 oz (225 g) fried tofu, cubed
• Herbs and vegetables: perilla, mint, shredded lettuce, bean sprouts, sliced banana blossom or split water spinach stems
• Lime wedges, sliced chili and mắm tôm (optional)

Allergens: crab and shrimp (shellfish), fish sauce, eggs and soy (tofu, soybean oil). This dish isn't suitable for anyone with a shellfish allergy.

Steps

1. Make or warm the broth. If using bones, blanch them in boiling water for 5 minutes, drain and rinse, then simmer in 10 cups (2.4 liters) fresh water with the dried shrimp for 1½ to 2 hours, skimming foam. If using stock, warm it with the dried shrimp for 20 minutes.

1. Mix the crab curds. In a bowl, combine the crab paste (oil included), ground pork, eggs, fish sauce and pepper. Stir until even. It will look loose; that's normal.

1. Cook the tomatoes. In a separate pan, heat a little oil and fry the shallots until fragrant. Add the tomatoes and cook 3 to 4 minutes until slightly soft. Set aside.

1. Form the curds. Bring the broth to a gentle simmer, not a rolling boil. Drop the crab mixture in by spoonfuls around the pot. Don't stir. Let it cook undisturbed 5 to 8 minutes until the curds rise and firm up.

1. Finish the broth. Gently add the tomatoes, fish sauce, sugar and tamarind or lime, then the tofu. Taste and adjust: it should be savory, a little sour and lightly sweet.

1. Assemble. Put a portion of vermicelli in each bowl, ladle broth over it and top with crab curds, tomatoes and tofu.

1. Serve with the herb plate. Let everyone add herbs, sprouts, lime and chili at the table, with mắm tôm in a small dish for anyone who wants it.

Tips for better curds

• Low heat is everything. A hard boil breaks the curds into a cloudy mess.
• Don't stir until the curds have set and floated.
• Annatto oil (optional): warm 2 tablespoons oil with 1 teaspoon annatto seeds for a minute, strain and drizzle on top for the color common in Southern bowls.

About mắm tôm

Mắm tôm is a pungent, purple-gray shrimp paste. Many people love it in bún riêu; others find the smell strong. It's often loosened with a little sugar, lime and chili before going into the bowl. Start with a small amount.

Make-ahead notes

The broth keeps in the fridge for 3 days and tastes even better the next day. Store the curds in the broth, and keep noodles and herbs separate so they don't go soggy. Reheat gently, again without boiling, to keep the curds intact.

Like other soups beyond phở, bún riêu is best eaten right away while the herbs are fresh. Keep the broth at a lazy simmer the moment the crab goes in, and the curds will rise on their own.