Cut the stems off your hatch chiles, then slice them lengthwise and remove the seeds. Slice the top and the root off your onion and remove the outer wrapper.
Bring a large pot of water to boil, then add the prepared hatch chiles and onion. Boil for 15 minutes.
When finished boiling, reserve 2 tablespoons of the water from the pot. Add that water to your blender along with the chiles, onion, vinegar, garlic cloves and salt. Blend until smooth.
Transfer blended hot sauce to bottles and store in the fridge. (I fit the yield of this recipe into five of these bottles.)
