First of all, chop out galangal, peeled shallots and fresh red chilli and grind them using a chopper or a grinding machine without adding water. Grind the ingredients till it turns into a fine paste.
Once the paste is ready, take a frying pan and put 2 tablespoons of sunflower oil/vegetable oil and heat the oil on a medium flame.
Once the oil is hot, add the fine-ground paste and stir it well till it turns aromatic. To this, add a ¼ teaspoon of dried red chilli paste and mix it well till the oil starts to separate.
After this, add the cleaned prawns keeping the tails for presentation purposes. Cook the prawns well in the paste for a minute till they are completely coated with the paste. Add 3 ½ cups of water and allow it to boil.
Meanwhile, pound just the white portion of the lemongrass stalks in order to have its aroma and taste in the soup. Then, carefully remove the midvein section of the kaffir lime leaves to have two pieces so as to add more flavour to the soup. As the soup starts boiling, add the prepared lemongrass and kaffir lime leaves.
To this, add 3 teaspoons of tamarind paste or solution with ½ a tea-spoon of salt to taste. If you are using a more concentrated solution, you need to add less according to taste. Traditionally, fish sauce is used as a substitute for the salt.
After this, add ½ a tea-spoon of light brown sugar. Now, just simmer the soup for about 8-10 minutes till the prawns are fully cooked.
Meanwhile, you can add hot Thai red and green chillies in the soup to taste. You may further taste the soup and add more salt is needed.
Next, add a tablespoon of lime juice to taste. Always make sure to taste the soup as you move ahead with adding the ingredients.
After the soup has rested for a while, remove the solids (stalks of lemongrass, kaffir lime leaves and the hot small chillies) to prevent the strong taste of any of these ingredients. Garnish the soup with freshly chopped coriander leaves and serve it hot.