1. Wash and break kaffir lime leaves into half. (Rubbing the leaves helps to release the flavor.)
2. Wash and peel off a small piece of galangal and cut into slices.
3. Then, wash and cut lemongrass into long pieces.
4. Rinse and wash oyster mushrooms. Then, cut the bigger pieces of oyster mushrooms into smaller pieces. Or, you can use your hands to tear off into smaller pieces.
5. Next, wash and cut Thai red chili peppers into pieces. ( You can add or reduce the amount of chili pepper according to your spiciness.)
6. After that, wash and cut limes into half. Then, squeeze fresh lime juice. (You can add more or less according to your taste.)
7. Remove shrimp heads and shells.
8. Put the shrimp heads and shells into a container and separate the flesh.
9. After, pour vegetable oil into the pot and turn on medium small fire.
10. Put the shrimp heads and shells into the pot and stir fry them a little bit.
11. Pour water into the pot. Cover the lid and let it simmer for 15 minutes.
12. After that, use a strainer to remove the shrimp heads and shells from the broth.
13. The following step, pour coconut milk into the shrimp broth and mix it well.
14. Put the sliced galangal from step 2 into the soup.
15. Then, add the cut lemongrass from step 3 into the soup.
16. Next, add Thai red curry paste into the soup. (You can adjust the amount of the chili paste according to your spiciness.)
18. Then, add the washed and cut oyster mushrooms from step 4 into the soup.
17. Put the washed kaffir lime leaves from step 1 into the soup. Let it simmer for 5 minutes.
20. Lastly, add the cut Thai red chili from step 5 into the soup and mix it. Then, turn off the fire and pour fresh lime juice from step 6 into the tom yum soup and mix it well. Sprinkle some cilantro before serving.
19. Put shrimp from step 8 into the soup. Then, add sugar, salt, fish sauce and mix it well.