Broil the chilies, garlic and shallots until soft and slightly charred. Peel the onions and garlic, carefully. It is important the you peel the darkest parts of the chilies as you do not want your Nam Prik to taste burnt, but you can leave most of the skin on though.
Pound the chilies, garlic and shallots into a coarse paste. You could also use a food processor with a pulse function, but remember not to overdo it. If you want to add Thai chilies this is the stage where they should be added, finely chopped.
Then simply add lime juice and fish sauce to taste. Serve with soft boiled vegetables and jasmine rice. I like to include some barbecued pork or barbecued fish too.
Remember that Nam Prik is not really considered to be just a condiment or sauce in Thailand. Nam prik is actually a dish of its own and should not be neglected if found on the table.