Heat a cast-iron skillet over low heat. Add chiles and garlic. Toast, turning often, until chiles are a shade darker and garlic is lightly toasted, about 4 minutes. Transfer both to a bowl.
Increase heat to high. Add tomatoes and toast, turning occasionally, until blackened on several sides, about 10 minutes, transferring to a bowl as done.
To make the salsa in a mortar, put toasted garlic and salt in a deep mortar (molcajete) and pound to a coarse paste, pushing down with the pestle and then rocking it back and forth a few times before pounding again. Add toasted chiles and coarsely crush, then pound in toasted tomatoes one at a time. Add salt to taste. To make in a blender, add all ingredients at once and pulse until coarsely puréed.