Preheat broiler and line a rimmed baking sheet with foil (do NOT use parchment, it will catch fire under the broiler).

Arrange the tomatillos, onion, garlic cloves and chiles in one layer on the prepared baking sheet. Broil veggies until they start to blacken. You'll have to keep an eye on them and remove things from the pan as they blacken (chiles first, then garlic, lastly onion and tomatillos -- approximately 5 to 15 minutes for everything to properly blacken).

Place blackened veggies and any pan juices in the food processor (can use a blender if you prefer). Add the cilantro, lime juice, and 1 tsp salt, then process until everything is chopped up and evenly distributed, making it as smooth or as chunky as you like.

Pour salsa into a container with a lid and place in the fridge to chill for at least 1 hour.

Before serving, check salsa for taste. Add more salt if you wish.

This makes around 3 cups of salsa. You can cook meats or eggs in it, or just use it as a condiment. As with any salsa, it will keep much longer if you portion out only the amount you need at 1 time, keep the rest of the salsa refrigerated, and always use a clean spoon to dish it out.