Adjust oven rack to upper-middle position and set oven to broil. Line a large, rimmed baking sheet with aluminum foil.
Place garlic, tomatillos, onion, and chiles on the baking sheet and drizzle with 1½ tablespoons olive oil. Set the baking sheet on the oven rack and broil the vegetables until the skins on the tomatillos have darkened and are partially charred.
2 unpeeled garlic cloves, 1 pound fresh tomatillos, 1 onion, 2-3 jalapeno chiles or 2 serrano chiles; stems removed, 3 tablespoons olive oil
Peel the garlic and scrape all the ingredients (including vegetables, juices & oil) from the baking sheet to a blender.
Add cilantro, sugar, broth, lime juice, kosher salt, and black pepper. Purée to desired consistency (I prefer the salsa fairly smooth).
¼ cup chopped fresh cilantro, ½ -1 teaspoon granulated sugar, ½ cup low-sodium chicken broth, 1-2 tablespoons fresh lime juice, ½ teaspoon coarse kosher salt, ¼ teaspoons freshly ground black pepper
In a medium saucepan, heat the remaining 1½ tablespoons oil and pour the tomatillo salsa into the pan. Set the heat to medium and bring the salsa to a simmer. Reduce heat to low and cook until mixture reduces to about 2 cups, about 10 minutes. Season to taste with additional sugar, salt, pepper and lime juice, if needed. The salsa is even better when made the day before serving. Keep refrigerated, up to 1 week, in an airtight container.