Toast the chiles in a small (8-inch) skillet over medium heat, stirring constantly until they’re aromatic and have darkened slightly, 1 1/2 to 2 minutes. Transfer them to a blender. In the same skillet, roast the garlic, turning regularly, until soft and blotchy-black in places, about 15 minutes. Cool, slip off the papery skin and add them to the blender jar.
Roast the tomatoes on a rimmed baking sheet 4 inches below a very hot broiler until splotchy black and soft, about 6 minutes. Flip them and roast the other side. Cool and add to the blender with the chiles and garlic and process completely smooth. Scrape into a serving dish and stir in enough water to give a spoonable consistency, usually 1/4 cup. Taste and season with salt, usually about 1 teaspoon. Refrigerated, the salsa will keep for several days.