Heat a dry griddle or heavy skillet over moderate heat. Toast the garlic, turning occasionally, until softened and blackened in spots, about 15 minutes. Let cool, then peel and roughly chop.
Meanwhile, preheat the broiler. Spread the tomatillos on a rimmed baking sheep and broil for about 8 minutes, turning once, or until blackened in spots and softened. Let cool on the baking sheet.
Scrape the tomatillos and any accumulated juices into a food processor or blender and add the chiles and roasted garlic. Puree until thickened and smooth. For a chunkier salsa, pulse the tomatillos and roasted garlic until coarsely pureed; finely chop the chiles and add them to the Tomatillo mixture. Transfer the salsa to a bowl and stir in 6 to 8 tablespoons of water, so the salsa has a spoonable consistence. Season with salt, plus a little sugar.
