Trim the stalks of the chillies and deseed – slice each chilli down its length, open up the chilli and scrape out the seeds with a teaspoon. It's important that you wear gloves for this task! The build up of chilli juice on your hands from these quantities will make your hands burn for days – DAYS!
Add all the ingredients except the sugar and salt to a high powered blender or food processor and blend until smooth. If your food processor isn't quite up to par, don't worry! You can sieve out any larger pieces after cooking.
Add the chilli mixture, the sugar and salt to a large saucepan and bring to the boil. Reduce the heat and simmer gently, stirring fairly regularly to stop the bottom sticking and burning. The sauce is done when the mixture is reduced and thickened, about 20 minutes of simmering. You can decide now how thick you want your sauce to be – add a little extra water if you want to thin it, or simmer a little longer if you want it thicker. Taste the mixture – this is quite a hard one to sample as it's pretty spicy and your palate will become blown out after a few tastes, but someone's got to do it! I added a little extra salt (1/2 teaspoon) and vinegar (1 teaspoon) for my tastes, but yours will be different. You might want some extra sugar, but for me the chillies were pretty sweet themselves.
Fill the bottle or jar you want to store your sauce in with boiling water and leave for 10 minutes. If you have used a high-powered blender, just decant the sauce into this clean bottle (a funnel is very useful here). If your blender wasn't quite able to purée the sauce and it still looks a little chunky, press it through a fine mesh sieve before bottling. Store in the fridge – it will last for several months.