Set an ungreased griddle or heavy skillet over medium heat. If using dried chiles, break off their stems. Toast the chiles a few at a time. Set them on the hot surface, press flat for a few seconds with a metal spatula. They'll crackle a little and become freagrant), then flip and press down to toast the other side. Transfer the toasted chiles to a bowl, cover with hot water, and set aside for 30 minutes, stirring regularly to ensure even soaking. Drain the chiles, discarding the liquid.
On a heavy, dry skillet or griddle over medium heat, roast the unpeeled garlic, turning occasionally, until blackened in spots and soft, about 15 minutes. Cool, slip off the papery skins, and chop roughly.
Preheat the broiler. Place the tomatillos on a baking sheet, and place about 4 inches from heat. When the tomatillos have blistered, blackened, and softened on one side, turn them over, and roast on the other side. Cool completely on the baking sheet.
Scrape the tomatillos and their juices into a food processor or blender, and add the rehydrated chiles and garlic, and puree to the desired consistency. Transfer salsa to a serving bowl, and add enough water to give the salsa an easily spoonable consistency, about 3 to 4 tablespoons. Season with salt, and add 1/4 teaspoon sugar (optional) if you want to soften any tartness.