Line a cookie sheet with foil. Pull the papers off a whole bunch of tomatillos, wash, and halve them. Place them cut side down on the cookie sheet. Throw a bunch of cloves of garlic, still in their paper, on the cookie sheet. Broil until the tomatillos begin to blacken--around 11 minutes in my oven, but keep an eye out, as I've heard some people's are done at 7.
After they've cooled sufficiently that you can handle them, peel the garlic cloves and pop them in the blender. Put the broiled tomatillos in the blender also. Blend. This mixture may be used immediately, kept in the fridge for a few days, or frozen for several weeks.
Cut up two or three pounds of pork butt/pork shoulder. Brown them in a little olive oil with as much onion, garlic, and oregano as you like. Do not skimp on the oregano. If you like jalapenos, this is where to add them. If you like potatoes, peel and chop a couple of potatoes and add that. Throw in 2-3 cups of broth (chicken, veg, whatever). If you like barley, dump in some barley. Add the tomatillo mixture.
Simmer all this until it looks like chili verde. Some people like it with a garnish of sour cream, fresh cilantro, avocado slices, a mild white cheese, whatever. It is forgiving stuff and will take all of these or none.