Chop the chillies roughly and put in a blender with the garlic, salt, sugar and water and blitz until a fine paste.
Pour the mixture into a jar and place in your larder with the lidslightly loose for a few days. When yo see bubbles staring to form it measns the chicllies are fermenting with the salt and sugar.
Add the vinegar and pour into a saucepan to simmer fro about 15 minutes until the sauce thickens. Once thicker, leave to cool and then blitz again with the blender.
Pour the blitzed sauce through a sieve into a sterilised jar for storage.