Warm 1 tbsp of vegetable oil in a deep saucepan, then add 2 tbsp of red curry paste. Let the curry paste cook for 2-3 minutes, stirring occasionally, then stir in 750ml of vegetable stock until evenly combined, and bring to the boil.
Peel and finely grate a 40g lump of ginger, then stir it into the vegetable soup together with (if you have them) 5 lime leaves.
Crush 2 stalks of lemongrass with a heavy weight, so they splinter, then add them to the soup and lower the heat and simmer for 15 minutes.
Put a saucepan of water on to boil and salt it lightly. Top and tail 100g of green beans. Cook the green beans for 3-4 minutes, until they are almost tender, then drain and set aside. Shred a head of pak choi.
When the soup has simmered for 15 minutes, squeeze 2 tbsp of lime juice into the soup, and add 2 tbsp of Thai or Vietnamese fish sauce. Add the green beans and the shredded pak choi, bring the soup back to the boil, and then ladle into bowls to serve. Finish with a few coriander leaves, and an extra lime half for squeezing over, if you like. Enough for 2.
Give the red curry paste a good 2 or 3 minutes in the hot pan before pouring in the stock. The heat will soften and mellow the more strident overtones of the coarse notes of the spice paste.
Although green beans and pak choi feel especially appropriate here, any green vegetable will work. The softer, more fragile leaves, such as spinach or spring cabbage are perfect. You can use chicken stock to give a richer, silkier texture to the soup.