Prepare the lemongrass (see the above video) and slice roughly. Blend together all the ingredients for the paste till you get a smooth green paste. This recipe will give you a mildly spicy paste. Increase the number of chillies if you want it spicier. Scrape down the sides of the blender in between to get all the ingredients to the bottom of the jar. If the lemon grass still looks fibrous, add another tablespoon of water and blend again. Store the curry paste in the fridge or use straight away.
Heat oil in a curry pot. Stir fry the green paste for 2 minutes with a cup of coconut milk to get a thick aromatic base. Add the vegetables (except the tofu) and sauté for a minute. Add the kaffir lime leaves and red chilli powder, if using. Add the water with the light soy sauce and salt. Cover and cook on medium heat for 2-3 minutes till the vegetables are cooked halfway. Add the brown sugar, remaining coconut milk, lime zest and tofu cubes. Simmer on low heat for 2 minutes. Taste and adjust the seasonings. Squeeze in the fresh lime juice.
Finish with some fresh basil and mint leaves and serve with rice or noodles