Set a large (10-inch) non-stick skillet over medium-high heat (if a non-stick skillet is unavailable, lay in a piece of foil). Lay in the garlic and tomatillos (cut side down). When the tomatillos are well browned, 3 or 4 minutes, turn everything over and brown the other side. (The tomatillos should be completely soft.)
Scoop the garlic and tomatillos into a blender jar or food processor with the chiles and 1/4 cup water. Process to a coarse puree. Pour into a salsa dish and cool. Thin with a little additional water if necessary to give the salsa an easily spoonable consistency. Taste and season with salt, usually a generous 1/2 teaspoon.