In the bowl of a food processor, combine chilies, garlic, brown sugar, and salt.
Blend until chilies are finely chopped and everything is evenly combined.
Transfer to a 32 oz jar, or two 16 oz jars, and pour over vinegar (¼ cup in each, if using 16 oz jars). Seal and store in a cool, dark, and dry spot for 3-5 days, until bubbles appear (I leave them in a cupboard).
When bubbles appear, open jars, stir, and reseal. Repeat for another 2-3 days.
Transfer jar contents into a blender. Blend until smooth.
Place a fine mesh sieve over a medium saucepan. Pour blender contents through sieve, in bathes, pushing it through with a rubber spatula. Discard pulp.
Bring to a boil over high heat, then reduce to a simmer and cook until sauce reduces to coat the back of a spoon, about 5-10 minutes.
Transfer to a clear jar. Allow to cool to room temperature then seal and store in the fridge.