Recipes adapted from Fiesta at Rick's and Mexican Everyday by Rick Bayless (W. W. Norton & Company; 2010 and 2005).
Heat a 10-inch cast-iron or nonstick skillet over medium-high. Add garlic and tomatillos. Cook tomatillos, cut side down, until well browned, about 4 minutes. Flip vegetables and cook until tomatillos are browned and completely soft and garlic is browned.
Transfer garlic and tomatillos to a blender or food processor, along with chiles in adobo sauce and water. Process to a coarse puree, about 5 seconds. Transfer to a medium bowl and let cool. Thin with a little more water if necessary. Season with salt.