To begin, prepare the curry paste. In a mortar and pestle, combine the soaked dried chilies, garlic, shallots, shrimp paste, and salt. Pound everything into a smooth paste. Alternatively, use a blender, adding a little water if necessary. This paste will form the base of your Gaeng Som, so ensure it's well blended.

In a large pot, heat 1 cup of water and 1 cup of vegetable stock over medium heat. Once it comes to a simmer, add the prepared curry paste. Stir well to dissolve the paste into the liquid, allowing the aromas to develop.

Add the tamarind paste and palm sugar to the pot, stirring to combine. This is where the characteristic sourness of Gaeng Som comes from. Adjust the level of tamarind to your taste preference for sourness, balancing it with the sweetness of the palm sugar.

Once the soup base is well combined and aromatic, add the fish sauce. Taste the broth and adjust the seasoning, adding more fish sauce or salt as needed. The soup should be a balanced mix of sour, salty, and slightly sweet.

Add the chunks of white fish to the simmering broth. Be gentle when adding the fish to avoid breaking the pieces. Cook for about 5-7 minutes until the fish is just cooked through and flakes easily.

Add the vegetables to the pot. Green beans are a classic choice, but you can also use carrots, cabbage, or other vegetables. Simmer for another 3-4 minutes until the vegetables are tender but still retain some bite.

For an extra touch of sourness, stir in the lime juice just before serving. This will brighten up the dish and give it an additional tang, though it's optional depending on your taste.

Serve the Gaeng Som hot, garnished with chopped cilantro. It pairs beautifully with steamed jasmine rice, which helps soak up the flavourful broth. Enjoy with a side of fresh vegetables or crispy fish cakes to complete the meal.