Before starting, wash well your hands and sanitize your knife, chopping board, blender bowl, jar.

Wash chili, de-stem and put with all other ingredients in the blender bowl (use food processor or stick blender if you don't have one). Blend till very fine texture.

Transfer to jar. I like to put a cloth held by a rubber band to allow better gas exchanges. Leave in a dark space (any cupboard is perfect) for 5-8 days. You will notice the mash bubbling and liquid separating at the bottom, this is normal. Stir with clean spoon every day.

When the bubbling has stopped (no more fermentation), strain through a fine mesh metal sieve, and use a spoon or scrapper to press the paste till only seeds and skin remain. 

Put the sauce into a sterilized jar ( boil in water for a few minutes and let cool down before filling). Keep in the fridge for many months.