How to cook banh canh cua: a sweet broth, just enough body and plenty of toppings

A good banh canh cua has a broth that is sweet from the bones and the crab, with a light body rather than a gluey one, chewy noodles, and the crab meat added at the end so it does not break up. This recipe for six bowls keeps the broth, the seafood preparation, the colouring and the blanching of the noodles clearly apart.

Quick facts

• Serves: 6 bowls.
• Preparation: 60 minutes.
• Simmering: 2 hours.
• Finishing: 30 minutes.
• Difficulty: fairly hard.

Ingredients

• 1.2 kg of pork or chicken bones.
• 2 sea crabs of about 800 g, or 400 g of cooked crab meat.
• 300 g of prawns and 300 g of pork trotter, optional.
• 1.2 kg of fresh banh canh noodles.
• Onion, daikon and shallot.
• Fish sauce, salt, rock sugar and pepper.
• Annatto oil, tapioca starch, spring onion, coriander and lime.

Choosing the ingredients decides the quality

Live crabs should be lively, with the apron tight and a solid feel; if you buy cooked crab meat it must be kept cold and must not smell of ammonia. Prawns should have glossy shells and springy flesh. The noodles should not be sour or slimy, and the bones should be fresh with no odd smell.

Prefer ingredients with a clear origin, still within their date and kept at the right temperature. Frozen food should be thawed in the fridge, in the microwave or under cold running water, not left on the worktop for hours. Vegetables eaten raw must be washed under clean running water, drained and kept apart from raw meat and fish.

Preparing and laying out before you turn on the heat

Blanch the bones for 5 minutes and rinse each piece and the pot. Clean the crabs safely, steam them and pick the meat on a clean tray; keep the shells to simmer briefly for flavour if you like. Devein the prawns. Mix the tapioca starch with cold water. Separate the fresh noodles gently and do not soak them for long.

Weigh the seasonings into small bowls and keep the utensils for raw and cooked food in two separate areas. Have a clean plate ready for the finished items; never put cooked food back on a plate that has held raw meat or seafood. Read all the steps through first, so the parts that have to be done quickly are not interrupted.

Step 1: simmer a clear broth

Put the bones, onion and daikon in with cold water, bring it close to the boil, skim, then keep the surface only trembling for 90-120 minutes. Do not stir the bones, and top up with boiling water when the level drops. Strain it into a clean pot before seasoning.

Step 2: cook the toppings separately

Boil or steam the prawns just until done and cool them; the pork trotter needs simmering until tender and up to a safe temperature. Keep the cooked crab meat aside and do not cook it from the start. Cooking each component to its own point keeps the broth clear and the toppings from turning rubbery.

Step 3: build the colour and the base flavour

Fry the shallot in a small amount of annatto oil and add it to the strained broth. Season with salt, fish sauce and a little rock sugar; the broth needs to be slightly stronger because the noodles absorb flavour. Do not let the annatto oil get so hot that it smells burnt.

Step 4: thicken it in a controlled way

Bring the broth to a gentle simmer, stir the starch slurry again and pour it in a thin stream while stirring the pot. Wait 30-60 seconds to see the real consistency before adding more. The aim is a broth that clings lightly to the ladle but still runs off in a stream.

Step 5: blanch the noodles and build the bowl

Blanch the noodles in a separate pot of boiling water according to their thickness, shake them dry and put them into a warmed bowl. Arrange the prawns, crab and trotter, ladle on the boiling broth and add the crab meat last. Scatter over spring onion, coriander and pepper.

Small tips that make the dish more consistent

1. Blanch and rinse the bones.
2. Simmer very gently.
3. Strain the broth before seasoning.
4. Steam the crab before picking the meat.
5. Cook each topping separately.
6. Use only a little annatto oil.
7. Mix the tapioca starch with cold water.
8. Wait for the thickening to show before adding more.
9. Blanch the noodles in a separate pot.
10. Add the crab meat at the end.

Every kitchen has a different hob power, pan thickness and level of moisture in the ingredients. The times are therefore only a reference; judge by colour, smell, tenderness, the rate of evaporation and the core temperature together. Note down the amount of liquid, the size of the equipment and the actual timings so it is easier to repeat next time.

Common mistakes and how to rescue the dish

The broth is cloudy

Let it settle and ladle the top through a straining cloth into a clean pot; next time lower the heat and do not stir the bones.

The broth is as thick as paste

Dilute it with hot, lightly seasoned stock and bring it back to heat; do not add more starch.

The noodles have gone mushy

They were soaked or blanched too long. Use a fresh batch and blanch bowl by bowl close to serving time.

The crab meat is shredded and dry

It was cooked too long. Keep the rest out of the pot and only put it in the bowl before you ladle on the broth.

A systematic way to taste and adjust

Taste a spoonful that has both liquid and a representative piece of the ingredients, let it cool for a few seconds and then work out whether the dish is short on salt, sweetness, acidity, richness or aroma. Change only one element at a time and wait until the seasoning has dissolved completely before tasting again. Fish sauce, salt, sugar and acid should go in a small amount at a time; this is far safer than trying to fix everything in one go.

If the dish is too salty, the real answer is to add suitable unsalted ingredients or liquid; adding sugar only masks the sensation and does nothing to the sodium. If it is too sweet, increase the liquid slightly and rebalance the salt before adding acidity. If the spices are harsh, take the solids out and let the dish rest rather than carrying on cooking it for a long time.

Controlling the heat and the equipment

The equipment has to suit the quantity: too wide a pot boils the liquid away quickly, too small a pot leaves the ingredients piled on top of each other, and a thin pan creates hot spots that burn. Heat it in a controlled way, watching the sizzle, the size of the bubbles and the rate of evaporation rather than just the position of the dial. When you need to top up a hot dish, use hot water so the cooking is not interrupted.

A food thermometer is a useful checking tool. Put the probe into the thickest part, away from bone and the base of the pan, and clean it before and after each reading. Poultry needs to reach 74C, minced meat 71C and fish 63C; for a dish where a direct reading is not practical, make sure every raw component is cooked through and the dish is held at a safe temperature.

Scaling the recipe up or down

For 12 bowls you can simmer one large pot, but blanch the noodles and boil the prawns in batches and split the broth into two pots for finishing, so you can control the thickness.

When you double the recipe, use wider equipment or work in batches so the food meets the heat in the same way as in the original recipe. Start strong seasonings at about 1.7 times and taste again, because the surface area for evaporation does not scale linearly. When you halve it, switch to a smaller pot to keep the depth of liquid and stop it drying out too quickly.

A schedule so the dish is ready on time

The stock, the base sauce and anything that needs marinating can be done in advance, following the storage guidance. The herbs, the frying, grilling, griddling and the assembly should be left until close to the meal. If you are cooking several dishes, work backwards from serving time: leave whatever has to be crisp or hot until last, and finish the cold work and the preparation first.

While you cook, clear away any utensil that has touched raw food straight away, change a dirty cloth and keep the worktop dry. For each batch, use the same ladle or weigh the portions so the results are even. Never taste with a spoon and then put that spoon back into the pot.

Serving and presentation

The bowl has the noodles, crab, prawns and trotter clearly arranged, with the lightly thickened broth around them. Serve the lime, chilli and neat fish sauce separately.

Warm the plates or bowls for a hot dish and chill them for a cold dessert. Leave some space around the food so the main components are easy to see. Herbs, nuts, fried shallots or a finishing sauce should only go on just before serving, to keep their colour and texture.

Preparing ahead and storing

Store the broth, the noodles and the toppings separately. Chill the broth and the seafood within 2 hours and use them within 3-4 days; reheat to 74C. Blanched noodles should be used straight away.

Cooked food should not stay at room temperature for more than 2 hours, or more than 1 hour when the surroundings are above 32C. Divide leftovers into shallow containers so they chill quickly and use them within 3-4 days; when reheating, bring the whole portion to 74C. Only reheat what you are going to eat, and throw away anything with an odd smell, sliminess or other unusual sign rather than tasting it.

Allergy and safety notes

The dish contains crab, prawns and fish in the fish sauce, and packaged noodles may contain wheat. Anyone allergic to crustaceans cannot share a broth that has been cooked with crab.

Pregnant women, young children, older people and anyone with a weakened immune system should eat food that is cooked right through, and should be especially careful about cross-contamination. Read the label on packaged seasonings, as fish, crustaceans, soy, wheat, egg, milk, sesame or peanut can appear in ready-made sauces.

A checklist for the finished dish

• The raw components have reached a safe temperature with no undercooked areas left.
• It smells as it should, with no old oil, burnt or oddly sour note.
• Salt, sweetness, acidity and richness are balanced when tasted at eating temperature.
• The main texture is what you were aiming for: tender without falling apart, crisp without being raw.
• The serving plate and the tongs are clean and have not touched raw food.
• The garnish went on close to serving time and the allergens have been announced.