You can decrease the heat by seeding the peppers, using fewer habañeros, or substituting some milder pepper. It does get less spicy as it cooks, so don't be alarmed if you make the salsa and it's overwhelming!
Preheat the broiler.
Pull the husks and stems off the tomatillos and rinse them. Cut the ends off all the peppers. Grease a large pan and put the tomatillos and peppers on it. Broil five minutes, turn, and broil five minutes more, until they are slightly charred.
Take the pan out and cover the peppers and tomatillos with plastic wrap or tin foil for ten minutes. When they are cool enough to handle, pull the skins off the peppers and tomatillos. At this point, you can remove the seeds from the peppers to decrease the spiciness if you want.
Put the skinned tomatillos and peppers in a food processor or blender with the onions, garlic, and cilantro. Purée.
In a heavy pot, heat some oil. Salt and pepper the pork chunks and brown them in the oil. You will need to do it in shifts so the pork has enough room and browns rather than simmering.
When all the meat is browned, put it all in the pot and add the puréed ingredients.
Simmer at a low heat for at least three hours until the meat is tender. If you want thinner chili verde, you can add chicken broth or beer. At some point, if you don't want the pork in large chunks, press the meat with the back of a spoon to make it collapse into shreds.
Spoon the chili verde into bowls, squeeze some lime juice over the top, and top with sour cream and fresh cilantro.