5 fresh serrano chiles
3 garlic cloves, unpeeled
1/2 cup fresh cilantro
1 large onion, coarsely chopped
2 teaspoons coarse salt
For tomatillos, remove husks and rinse under warm water to remove stickiness. If using canned tomatillos, drain and measure out 2 cups. Broil chiles, garlic, and fresh tomatillos (do not broil canned) on rack of a broiler pan 1 to 2 inches from heat, turning once, until tomatillos are softened and slightly charred, about 7 minutes.
Peel garlic and pull off tops of chiles. Purée all ingredients in a blender.