In a large pot, heat the vegetable broth over medium-high heat until it reaches a gentle boil. Reduce heat to low.
Add the coconut milk, and stir.
Slice the ginger. Tear the kaffir lime leaves into pieces. Lightly crush the lemongrass stalk and chop it into big pieces. Add all these to the pot.
Simmer for about 7–8 minutes.
Add in the chili peppers, sliced tofu, sliced mushrooms, soy sauce, brown sugar, and salt to the pan. Let it simmer for a further 5 minutes or until the mushrooms are cooked.
Now take the pot off heat and add in the lime juice 1 tbsp at a time, give it a taste and add more if desired.