600ml chicken or vegetable stock
2 stalks lemongrass, trimmed and finely sliced
2 shallots, finely sliced
1 red chilli, finely sliced
100g mushrooms (oyster, shiitake,chestnut), finely sliced
1 tsp sugar
4 x 150g salmon fillets, skin on
1 tbsp vegetable/groundnut oil
100g baby spinach, washed
2 tbsp fish sauce
1 tbsp lime juice, plus 1 lime quartered to serve
Put the stock, lemongrass, shallots, chilli, mushrooms and sugar into a saucepan over a medium heat and bring to a simmer. Cook for 10 minutes.
Meanwhile, halve each salmon fillet lengthways and season well. Heat the oil in a non stick frying pan over a medium heat. When hot, add the salmon, skin side down and sear for 2-3 minutes until the skin is crisp. Turn over and continue to cook for a further 2 minutes, until heated through but still pink in the middle.
Wilt the spinach in the broth for 10 seconds then remove with tongs and divide between four warm shallow soup bowls. Arrange the salmon on top. Add fish sauce and lime juice to the broth then spoon round the salmon. Serve with a wedge of lime to squeeze over.