Place the tomatillos, chile, the half onion, and the garlic on a vegetable grilling tray. Grill over medium high flame, turning the veggies over as they blacken. Grill until the tomatillos begin to soften. The garlic and chile will be done first--pull them off the grill. Alternatively, line a baking sheet with foil. Roast the tomatillos and chiles close to the broiler flame, until slightly blackened on all sides. You will need to move things around to get them evenly charred.

If you broiled the tomatillos instead of charring on the grill, you will want to char the onion and garlic in a hot cast iron skillet or comal. On a stovetop, heat the comal or cast iron skillet on high flame. Toast the garlic on all sides, and the onions, cut side down until nicely charred.

Puree all the charred veggies together in a blender. Add the cilantro and salt; blending just until there are bits of cilantro throughout the salsa.

Pour into a jar. Keep refrigerated.