How to Make It
Adjust an oven rack to 4 inches below the broiler and preheat the broiler to high. Scatter the tomatillos, onion halves and peppers on a foil-lined rimmed baking sheet. Broil until they’re charred and blackened on top and the tomatillos are completely tender, 6 to 12 minutes. Transfer the vegetables and any accumulated juices to a blender, food processor or the cup of an immersion blender. Add half of the cilantro. Pulse until a coarse puree is formed.
In a medium saucepan, heat the oil over high heat until shimmering. Pour the salsa into the hot oil all at once (it will steam and sputter). Immediately start stirring and cook, stirring, until the salsa is darkened and thick enough to coat the back of the spoon, about 3 minutes. Remove from the heat. Finely chop the remaining cilantro and stir it into the salsa. Season to taste with salt. Let cool, then serve. The salsa can be refrigerated for up to 5 days.