Remove the papery husks from the tomatillos. Rinse the tomatillos under cold running water to remove the sticky residue. Place the tomatillos, onion, jalapeño, garlic, and cilantro in a food processor and pulse until finely chopped. Pour the salsa into a medium skillet and cook over medium heat until softened and uniformly colored, about 5 minutes. Season with the salt and pepper. Stir in the lime juice (if using).
Tip: This slightly tangy green sauce goes well with grilled or roast chicken and pork and rice. You can also shred any leftover chicken or pork, toss it with the salsa, and make soft or hard tacos.