Roast the chilis, aubergine, garlic and shallots by wrapping them into tin foil packets. The foil will keep in the juices. Place the foil packets in a frying pan and fry until the vegetables are soft and cooked. Remove the skin and seeds from the peppers. Finely chop shallots, garlic and peppers, add the coriander leaves, fish sauce and lime juice until well combined in a mortar. This leaves you with a salsa that is slightly chunky and a little soupy. You can also put every thing into a food processor and it will give you a rather smooth salsa. Let stand at least 30 minutes before serving to let all of the flavours meld.