Place tomatillos, onion, garlic, and jalapeno peppers into a saucepan over medium heat, and pour in enough water to cover. Bring the mixture to a boil, reduce heat, and simmer until the tomatillos soften and change color from bright green to a yellow-green color, approximately 5 to 8 minutes.

Using a slotted spoon, transfer vegetables to a blender, filling the pitcher no more than halfway full. Hold down the lid with a folded kitchen towel, and carefully start the blender with a few quick pulses to get the mixture moving. Puree until smooth, about 60 seconds. Mix in salt, cilantro, and lime juice, and blend again for a few seconds to combine.