Salmon in lime broth

For ➋
30 cl chicken or vegetable stock*
1 lemongrass stalk, trimmed, peeled, white part finely sliced 
2 shallots, peeled, finely sliced 
1 mild fresh red chili, finely sliced 
100 g mushrooms (oyster mushrooms or fresh shiitake), finely sliced 
1 ts sugar** 
1 tbs vegetable oil 
2 150 g fresh salmon fillets, with skins, bones removed 
sea salt & freshly ground black pepper 
100 g (baby) spinach leaves 
1 tbs (Thai) fish sauce 
1 tbs fresh lime juice 

Bring the stock to the boil in a large saucepan. Add the lemongrass, shallots, chili, mushrooms*** and sugar. Reduce the heat. Simmer for 10 m. ***
Meanwhile, heat the oil in a frying pan. Sear the salmon fillets, skin-side down, until the skin is crisp. Turn once and cook briefly on the other side, leaving the inside slightly pink. Remove from the heat and season with sea salt and freshly ground black pepper. 
Boil the spinach in the hot broth for 5 s, remove with a slotted spoon and arrange in warmed shallow soup bowls. 
Place the salmon on top. 
Add the fish sauce and lime juice to the broth, and spoon it around the salmon.

* Use a miso based broth instead (use 1 tbs miso paste for 30 cl water)
** Optional
*** Add mushrooms for the last 3-4 m for a meatier mushroom