Set a large (10-inch) nonstick skillet over medium-high heat; if you don't have a non-stick skillet, 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 along with the chiles and 1/4 cup water. Process to a coarse purée. Pour into a dish and let cool.
Thin the salsa with a little additional water, if necessary, to give it an easily spoonable consistency. Taste and season with salt, usually a generous 1/2 teaspoon.