Place the whole peeled tomatillos, garlic, jalapenos, and quartered onion pieces in a shallow baking dish. and roast under the broiler for about 10 minutes, turning half way, until vegetables are charred on the outside.
Take them out of the oven and let them cool for about 10 minutes. Pull the stems from the jalapenos, Remove the peel from the garlic, it should just squeeze out. Add everything into a blender. Make sure to also add the juices from the baking dish that seeped out during cooking.
Add the cilantro, salt, and lime juice to the blender as well. Blend to your desired consistency. I prefer a smoother salsa, but you can also just pulse a few times for a thick and chunky salsa. It should keep for between 5-7 days.