Step 1

Adjust oven rack to 4 inches below broiler and preheat broiler to high. Place tomatillos, onion, and chilies on a foil-lined rimmed baking sheet. Broil until darkly charred and blackened on top and tomatillos are completely tender, 6 to 12 minutes

Step 2

Transfer vegetables and their juice to a blender, food processor, or the cup of an immersion blender. Add half of cilantro. Blend in pulses until a rough puree is formed.

Step 3

Heat oil in a medium saucepan over high heat until shimmering. Pour salsa into the hot oil all at once (it will steam and sputter). Immediately start stirring and continue to cook, stirring, until salsa is darkened and thick enough to coat the back of the spoon, about 3 minutes. Remove from heat.

Step 4

Finely chop remaining cilantro and stir into salsa. Season to taste with salt. Let cool, then serve. Salsa can be stored in the refrigerator for up to 5 days.