Preheat the oven to 450 degrees F.
Spray a baking sheet with cooking spray and place the tomatillos, quartered onion and garlic cloves on the baking tray. If using a jalapeño, add it to the baking tray with the other vegetables.
Roast the vegetables for 20 minutes flipping the vegetables at the 10 minute mark. The tomatillos should be lightly charred and the onion beginning to brown.
Transfer the roasted vegetables and roasted Hatch chiles (or jalapeño) and any remaining juice on the baking sheet to a food processor or blender. Blend until almost smooth.
Add the cilantro leaves and kosher salt and pulse a few more times until mixed.
Serve the salsa topped with cotija cheese if desired and yellow or white corn tortilla chips for dipping.
