Set your oven to broil. Remove the outer casings from the tomatillos. Wash and throughly dry the tomatillos and green chiles.
Lightly coat the chiles and tomatillos with a neutral oil and place them in a roasting dish. Roast for 10-15 minutes or until the tomatillos are soft and the peppers are blistered, flipping as needed.
Carefully move the chiles to a bowl and cover with a plate or plastic wrap to let steam for 10 minutes. Rub the skins off the peppers, stem and seed (if you want a less spicy salsa).
Place the peppers, with the roasted tomatillos, onion, garlic, and cilantro into a blender. Purée, taste, and season with salt.
