Tomatillos and fresh chiles give this salsa a bright, “green” flavor, and toasting the ingredients contributes a smoky element (plus it loosens the chiles’ skins).
1/2 pound tomatillos, husked and rinsed
1 thick onion slice
1 large poblano chile
1 1/2 medium serrano chiles
1/2 ripe avocado (optional), peeled
2 tablespoons coarsely chopped cilantro
1 whole garlic clove
2 tablespoons fresh lime juice
About 3/4 tsp. kosher salt
Preheat broiler and set a rack 3 in. from heating element. Line a rimmed baking pan with foil and set tomatillos, onion, poblano, and serranos in it.
Broil the vegetables, turning as needed, until tomatillos and onion are speckled brown and chiles are black all over, 12 to 15 minutes; as vegetables are done, transfer to a bowl. Cover vegetables with a plate or foil and let stand about 5 minutes for chile skins to loosen. Pull off stems and blackened skins from chiles; for best flavor, don’t rinse chiles (a few blackened bits are okay to leave on). Open poblano and remove seeds.
In a food processor, pulse vegetables and any juices; avocado, if using; cilantro; and garlic until coarsely puréed. Scrape into a bowl and stir in 1/4 cup water, lime juice, and 3/4 tsp. salt. Season to taste with salt.