Move the oven rack to the highest position and preheat the oven to broil. Line a baking sheet with aluminum foil and spray it with cooking spray.
Clean and remove the husks from the tomatillos.
Cut the jalapeno through the middle lengthwise and remove the seeds and membrane with a spoon.
Remove the stem from the serrano pepper and jalapeno pepper. Peel the garlic cloves and quarter the onion.
Wash the cilantro thoroughly.
Place the tomatillos and garlic cloves onto the roasting pan. Season with salt and pepper and drizzle with olive oil.
Place the pan into the oven and roast, use tongs to turn as necessary. Broil the ingredients are charred, around 8-10 minutes.
Remove the tomatillos from the oven, and allow them to cool slightly.
Pour the charred tomatillos and garlic cloves into a food processor or blender along with the quartered onion, peppers, cilantro, lime juice, seasonings, olive oil and pan juices. Pulse in the blender until your desired consistency is reached.
To thin the salsa, add cold water 1 tablespoon at a time.
Puree until chunky smooth. Adjust the salt and pepper if needed.
Serve as a condiment or with tortilla chips for dipping.
This salsa can be stored for 2-3 days before serving tightly covered in the refrigerator.