Tom yum soup with prawns and mushrooms
A clear Thai hot-and-sour soup with fragrant lemongrass, galangal and makrut lime leaves, tender mushrooms and juicy prawns. Finish with fish sauce and fresh lime juice off the heat for a bright, punchy broth.
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Servings
Originally developed for 4 servings.
Ingredient checklist
Method
- No timer needed
Bruise the lemongrass with the flat of a knife and cut into 5 cm lengths. Thinly slice the galangal and tear each makrut leaf once. Bruise 2 chillies; thinly slice the remaining chilli for serving. For milder soup, use only 1 bruised chilli. Tear the mushrooms into roughly 3 cm pieces and roughly chop the coriander. Squeeze and measure the lime juice, keeping 45 ml and 15 ml separate; measure 30 ml and 10 ml fish sauce separately. Keep the drained prawns refrigerated until step 5, separate from the garnish and serving utensils. Wash hands and clean equipment after any contact with raw prawns.
- 10:00
Put the stock, lemongrass, galangal, makrut leaves and bruised chillies in the saucepan. Bring just to the boil over medium-high heat, allowing about 5 minutes. Reduce to a gentle simmer, partially cover and infuse for 10 minutes. Avoid a rolling boil or heavy reduction.
- No timer needed
Lift out and discard the lemongrass, galangal, lime leaves and bruised chillies using a slotted spoon or small sieve. If the broth has noticeably reduced, add enough water to restore approximately its starting level, up to 150 ml.
- 05:00
Add the mushrooms and sugar. Return to a gentle simmer, then cook uncovered for 5 minutes, until the mushrooms are tender but still hold their shape.
- 03:00
Add the cold prawns and gently stir them through the broth. Allow it to return to a gentle simmer, then cook for 3–4 minutes, checking after 3 minutes. The prawns should be firm and opaque throughout, with no translucent centre. Check the thickest part with a fine-tip thermometer: it should reach 75°C and remain there for 30 seconds; cook longer if necessary. Do not rely on pink colour or curling alone.
- No timer needed
Take the pan off the heat immediately. Stir in the initial 30 ml fish sauce and 45 ml lime juice; if your stock is salted, start with less fish sauce. Taste a slightly cooled spoonful, then add the reserved fish sauce and lime juice a little at a time as needed. Aim for pronounced sourness balanced by savoury saltiness, not sweetness. You may not need all the reserves.
- No timer needed
Divide the prawns and mushrooms evenly between four bowls and ladle over the broth. Scatter with the prepared coriander and add the sliced chilli to taste, or offer it separately. Serve straight away rather than holding the soup at a simmer.
Chef tips
- If the broth tastes sour but flat, try a little reserved fish sauce before adding more lime.
- For modest oversalting, dilute with a little hot water and reassess the lime balance; sugar will not remove excess salt.
- Start with fewer infused chillies if unsure. Removing chillies later cannot remove heat already extracted into the broth.
- Keep the infusion gentle and partially covered. Replace evaporation before the final seasoning, not afterwards.
- If the prawns need longer to reach the temperature endpoint, continue gently cooking and delay seasoning and serving accordingly.
Equipment check
- 3-litre saucepan, approximately 20–22 cm wide, with lid
- Chopping board and knife
- Scales and measuring jug
- Citrus juicer
- Slotted spoon or small sieve
- Fine-tip digital food thermometer
- Ladle and four heatproof bowls, each at least 500 ml
Tags
Behind the dish.
Overview
This is tom yum goong nam sai: the clear version of Thai prawn soup, without coconut milk, evaporated milk or roasted chilli paste. A brief, gentle infusion extracts the aromatics without heavily reducing the broth. Cook the prawns last, then add lime juice off the heat. The result should be distinctly sour, savoury and fragrant, with adjustable chilli heat and firm, juicy prawns. Makes four light soup portions.
Ingredient notes
Choose ready-made clear, unsalted or very low-salt prawn or fish stock without strong wine, tomato or herb flavours. Water can replace the stock, though the broth will be lighter. Ordinary stock cubes are often too salty at their standard dilution.
Fresh or frozen galangal and makrut lime leaves give the intended fragrance; use frozen aromatics directly from frozen. Ginger and ordinary lime leaves are not equivalent substitutes. Oyster mushrooms can be replaced with the same prepared weight of fresh shiitake caps, tough stalks discarded and caps sliced 5 mm thick.
Start with chilled, thawed prawns. If buying frozen, thaw in a covered container in the fridge according to the packet before starting this recipe, then drain and weigh. Prawns contain crustaceans; fish sauce contains fish. Stock may also contain molluscs, celery or wheat. Check labels, including for dairy if required; do not assume stock or fish sauce is gluten-free.
Serving & storage
Serve immediately in four bowls of at least 500 ml capacity, with sliced chilli offered separately if preferred. Remove the tough infusion aromatics before serving.
Cool leftovers promptly in shallow portions and refrigerate within 2 hours at 5°C or colder. Use within 48 hours or freeze sooner, observing any shorter ingredient-label limit. Thaw frozen leftovers in the fridge. Reheat only once, until the broth and solids are steaming hot throughout, then serve immediately; reheating will make the prawns firmer.
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