Chipotles make this salsa rich and smoky. Serve it as a topping for the tacos or as a dip for tortilla chips.
Working in 2 batches if needed, cook tomatillos and garlic in a large skillet (preferably cast-iron) over medium-high heat, turning occasionally, until charred on all sides, 15 to 20 minutes. Transfer to a plate, and let cool slightly. Peel garlic. Finely chop tomatillos and garlic.
Mix together tomatillos, garlic, chipotles, sugar, and 1/2 teaspoon salt.