Preheat the oven to 425°.
Remove the husks from the tomatillos. Briefly rinse the tomatillos under cold water.
Evenly spread them on a sheet tray lined with parchment paper with onion, garlic, and peppers.
Drizzle the olive oil over top of the vegetables. Season with salt.
Place on a rack in the top ⅓ of the oven at 425° and cook for 20 to 25 minutes or until lightly browned and the tomatillos and peppers turned to a muted green color.
Remove them from the oven and let them rest for 10 minutes.
Transfer to a blender with a lid but replace the center piece of the lid with a kitchen towel and blend on medium speed until smooth.
Adjust the seasonings with salt and serve.
