8 oz. tomatillos, husked and rinsed
6 cloves garlic, peeled
3 dried chipotle chiles, stemmed
1⁄2 tsp. kosher salt
Heat oven to 500°. Place tomatillos on a foil-lined baking sheet and roast, turning halfway through cooking, until blackened in spots and cooked through, about 20 minutes; let cool.
Meanwhile, heat a 12″ cast-iron skillet over medium-low heat; add garlic and chiles, and toast, turning, until chiles and garlic are blistered and blackened in spots, about 10 minutes. Transfer to a blender along with tomatillos, salt, and 1⁄2 cup water; blend until smooth. Let cool.