Bring a pot of water to a boil. Remove husks from tomatillos and rinse well. Cook the tomatillos in the boiling water until soft, 5 to 8 minutes. Drain and set aside.Advertisement
Toast garlic cloves, jalapeno and onion in a dry medium skillet over medium heat, turning occasionally, until browned, fragrant and soft, 5 to 7 minutes.
When cool enough to handle, peel the garlic. Remove the jalapeno stem and remove seeds if desired. Combine the tomatillos, garlic, jalapeno, onion and avocado in a blender or food processor. Process until smooth. Stir in cilantro, salt and pepper.
Make Ahead Tip: Cover and refrigerate for up to 2 days.