From Cookie And Kate
1 ½ pounds tomatillos (about 12 medium), husked and rinsed
1 to 2 medium jalapeños, stemmed (omit for mild salsa, use 1 jalapeño for medium salsa and 2 jalapeños for hot salsa, note that spiciness will depend on heat of actual peppers used)
½ cup chopped white onion (about ½ medium onion)
¼ cup packed fresh cilantro leaves (more if you love cilantro)
2 tablespoons to ¼ cup lime juice (1 to 2 medium limes, juiced), to taste
½ to 1 teaspoon salt, to taste
Optional variation: 1 to 2 diced avocados, for creamy avocado salsa verde
Preheat the broiler with a rack about 4 inches below the heat source. Place the tomatillos and jalapeño(s) on a rimmed baking sheet and broil until they’re blackened in spots, about 5 minutes.*
Remove the baking sheet from the oven, carefully flip over the tomatillos and pepper(s) with tongs and broil for 4 to 6 more minutes, until the tomatillos are splotchy-black and blistered.
Meanwhile, in a food processor or blender, combine the chopped onion, cilantro, 2 tablespoons lime juice and ½ teaspoon salt. Once the tomatillos are out of the oven, carefully transfer the hot tomatillos, pepper(s) and all of their juices into the food processor or blender.
Pulse until the mixture is mostly smooth and no big chunks of tomatillo remain, scraping down the sides as necessary. Season to taste with additional lime juice and salt, if desired.
The salsa will be thinner at first, but will thicken up after a few hours in the refrigerator, due to the naturally occurring pectin in the tomatillos. If you’d like to make creamy avocado salsa verde, let the salsa cool down before blending in 1 to 2 diced avocados (the more avocado, the creamier it gets).
*A note from Rae: I've read that simmering the tomatillos instead of roasting them makes them a little less sweet. If that's to your taste, here is a slightly different version to try.