Pour stock into a deep cooking pot and turn heat to medium-high.
Add processed lemongrass to the pot, including the parts of the lemongrass stalk you didn't slice, kafir leaves, ginger, galic and chilli.
High simmer for 5 minutes, or until fragrant.
Add 2 cup thin sliced mushrooms to broth along with tin of coconut milk and lime juices. Continue cooking gently (lowest setting) for another 8-9 minutes.
Add shrimp, bell pepper, coriander and cherry tomatoes (if using). And cook on low 5-6 minutes more. Add 1 cup remaining sliced mushrooms and a few whole ones as well, then cook on low for 4-5 minutes. Add extra coriander at this stage if you love the taste (like I do)
Add fish sauce, stir and then test the soup for spice and salt, adding more chili and/or fish sauce (instead of salt) as desired. If too sour for your taste, add your sugar at this stage; if too salty, add a squeeze of lime juice. Add more coconut milk if you want your soup richer/creamier, or if it's too spicy for your taste.
Serve in bowls with fresh coriander sprinkled over. Enjoy!! (See below for more variations on this recipe.)