This Asian soup is substantial enough to serve as a smart supper, but is also lovely as a dinner party starter, providing it's not followed by too heavy a main course. I like to use pak choi, but you could use spinach.
Boil a kettle of water. Cut the salmon widthways into 1 cm wide slices. Place in a bowl and squeeze over the lime juice: set aside for 20 minutes.
Meanwhile, place the noodles in a large bowl, cove with the boiling water and set aside.
Heat the oil in a large wok, throw in the ginger, garlic and shallots and cook for 3-4 minutes unti softened. Pour in the stock and coconut milk, then bruise the lemon grass with a rolling pin - a quick bash or two should do it - and add to the pan with the curry paste. Stir well. Then bring the soup to the boil, reduce the heat and simmer very gently for 5 minutes.
Add the salmon, pak choi and soy sauce and simmer for another 2-3 minutes until the pak choi is tender, but still crunchy.
Drain the noodles and divide between 4 bowls. Ladle over the soup, then float a chilli ring or two in each bowl. Serve immediately.