Add the chillies, garlic and spices to a large sterilised Kilner jar along with the salt and water and leave to ferment for a week and half. It should start to bubble after a few days, which is how you know it's fermenting. Open the lid to allow the built-up gas to escape every few days.
Once fermented, strain the contents of the jar but reserve the liquid.
Blitz the chillies and garlic in a food processor until roughly chopped, adding a splash of the fermenting liquor to get it going. I suggest you start by blitzing half to a roughly chopped paste, then blitzing the other half entirely with 200ml of the fermenting liquid, to make a smooth sauce. You can then decide which you prefer (for me, it’s the paste).
Transfer to sterilised jars and keep in the fridge for up to 3 months.