I got this base recipe from a vegan friend. If you can't find one of these peppers, swap in another one!
You're in charge of the heat here. For a milder salsa, remove all the ribs and seeds inside the peppers. For medium, leave in a few ribs, and for hot, go nuts. Rough chop the peppers and tomatillos, then throw into a blender or food processor with salt and lime juice. Pulse to desired consistency.
As with most salsas, this will taste better if you let it sit in the fridge for a few hours before eating. It's great on chips or drizzled over steak or pork tacos.