Place the oven rack on the highest rack setting. Preheat the broiler (500 degrees F) while you prep the ingredients. Remove the papery husks from the tomatillos (2 lbs), and rinse well with warm water to get rid of the stickiness. Pat dry with a clean kitchen napkin.
Transfer the tomatillos, onion wedges (about 1 small onion), 5-6 garlic cloves (skin on), and 2 serrano peppers on a rimmed baking tray. Drizzle about 1 tbsp oil, and sprinkle salt. Toss the ingredients to coat well.
Place the baking tray on the topmost rack, and broil for 4-5 minutes, or until charred on top.
Flip the vegetables, and char the other side for another 4-5 minutes. Keep a close eye during the broiling process or you may end up burning the veggies.
Remove the baking tray from the oven and place on a cooling rack, set aside until cool enough to handle.
Once cool enough, transfer the roasted tomatillos, onions, chile peppers in the bowl of a food processor or into a blender. Remove the garlic from the skin and add it to the processor along with any juices that may have collected on the tray. {For mild salsa, remove the seeds from the roasted serrano peppers, save the seeds if you want to add some heat to the salsa after blending in step 6}. Add a handful of cilantro, 2 tbsp lime juice, and 1/2 tsp salt.
Pulse until all the ingredients are coarsely combined. You can leave it chunky or thin it out with some water for a smooth salsa. I did not add any water. The juices from the roasted tomatillos were enough to blend the salsa. Season to taste and adjust with more salt, sugar, serrano chile seeds or lime juice if desired.
Chill salsa in the refrigerator for about 2-3 hours, this allows the flavors to mingle to deepen, serve with chips or in any of your favorite Mexican recipes.