Remove the papery husks from the tomatillos and rinse well. (The tomatillos will feel a little sticky; this is normal.) Preheat the broiler. Cut the tomatillos in half and place them and the pepper cut side down on a foil-lined, rimmed baking sheet. Tuck the garlic cloves (in their skins) in between the tomatillos.
Place about 4 inches under the broiler for 3-5 minutes, checking on the early side, to lightly blacken the skins of the tomatillos in spots.
Remove the baking sheet from the oven, carefully flip the tomatillos, pepper, and garlic and broil for 3-5 more minutes, checking again on the early side, or until the tomatillos are lightly blistered and have a few more charred spots. Remove from the oven, and when cool enough to handle, remove the garlic skins and discard.
Place the broiled tomatillos, pepper, garlic, onion, cilantro, and lime juice, and salt (starting with 1 tablespoon of lime juice and ½ teaspoon of salt) in a blender or food processor and pulse or blend until all ingredients are finely chopped and the mixture is mostly smooth, scraping down the sides as needed. Season to taste with more lime juice and salt. (I tend to use 1½ tablespoons lime juice and between ¾ and 1 teaspoon kosher salt. The flavors will meld and improve over time.)
The salsa will thicken slightly over time due to the natural pectin in the tomatillos. When stored in a jar or airtight container in the refrigerator, the salsa will maintain freshness for at least 1 week. Give the salsa a quick stir before serving.
Serve with chips or as a salsa accompaniment anywhere you would use red salsa.