How to Make It
Heat a large cast-iron skillet. When it is very hot, add the tomatillos, garlic cloves, tomatoes and onion and cook over low heat, turning frequently, until blackened in spots and softened, 8 to 10 minutes. Transfer the vegetables to a plate and let cool.
Put the tomatillos, garlic, tomatoes and onion in a food processor and pulse until coarsely chopped. Add the chipotles and adobo sauce, cilantro, salt and sugar and pulse just until combined.