This sauce is very similar to the Thai product known as "chilli paste in soybean oil"†, which in itself is great stuff, but if you can't buy it in your area, or you like to tinker in the kitchen, try this recipe.
Although it will take some time, you will be rewarded with a big bucket of dark sweet chilli paste that lasts for ages. Enlivens stir fries, soups and grilled dishes. Makes 1 litre
Heat the peanut oil in a large, heavy based pot. Fry the onions, garlic, galangal and lemongrass over medium heat, stirring occasionally, until soft and starting to colour. This takes about 20 minutes so turn down the heat if it begins to colour too quickly.
Add the capsicums, chillies and tomatoes, stir and reduce the heat slightly. Cook the vegetables gently until the are collapsed and beginning to caramelise. This takes several hours so stir every now and then to make sure it does not catch on the base of the pot. Add the palm sugar and fish sauce and cook for another hour or so. By this stage the vegetables should be completely collapsed and very deeply coloured. Remove from the heat.
When the mixture has cooled slightly, puree in batches in a food processor. Don't drain any oil from the jam, it is needed to achieve the required colour and will be cooked out anyway. Rinse out the pot and return the jam to a low/medium heat and cook until the colour is a deep red and the oil has separated, about another hour. Stir frequently as it will burn easily at this stage. Drain off the oil and spoon into sterilized jars. Cool and refrigerate until required. Lasts at least 1 year, probably more.
* To trim lemongrass, cut off the top ¼ and woody base from the stem and peel off the outer layer.
** Remove the seeds if you can't stand the heat.
† Anthropod has a fabulous recipe for nam prik phao, which is much closer to the original Thai product. Why not try making both?
Because this paste is fully cooked, you can eat it as is. A dollop on grilled fish or chicken is yum!