Place the tomatillos, jalapeños, and garlic cloves in a medium saucepan. Cover with water and bring to a boil over medium-high heat. Once boiling, reduce heat and simmer for 10 minutes until the tomatillos are soft and just beginning to turn olive-colored but still holding their shape.
Using a slotted spoon, transfer the tomatillos, jalapeños, and garlic to a bowl. Discard the cooking water. Let cool for at least 20 minutes until no longer steaming — adding hot tomatillos directly to the avocado will dull the bright green color and muddy the flavor.
Transfer the cooled tomatillo mixture to a blender. Add the roughly chopped onion, cilantro, avocados, lime juice, and salt.
Blend until completely smooth, about 30–45 seconds. Taste and adjust — more salt if flat, more lime if it needs brightness. Serve immediately with tortilla chips or as a taco topping, or press plastic wrap directly onto the surface and refrigerate until ready to use.
Notes
Three jalapeños with seeds makes this genuinely spicy. For medium heat, remove the seeds and white membrane from all three before boiling. For mild, use one or two jalapeños seeded. The tomatillos' natural acidity amplifies heat perception — start conservative if cooking for a crowd.
Hot tomatillos blended directly with avocado will turn the salsa brownish-green and slightly dull in flavor. 20 minutes of cooling preserves the bright green color that makes this salsa visually striking.
The avocado should yield slightly to gentle pressure but not feel mushy. An underripe avocado will leave the salsa tasting grassy and slightly bitter.
If the salsa is too thin, add half an additional avocado and blend again. If too thick, add cooking liquid 1 tablespoon at a time.
Press plastic wrap directly onto the surface of the salsa (no air gaps) and refrigerate up to 2 days. The lime juice slows browning but won't prevent it entirely — this is best eaten fresh or within 24 hours for best color.