Pozole Verde

1. If you happen to be using a pig's head, submerge it in water in a very large pot and bring to a boil. Add the nixtamal, if using. Drop the heat to a gentle simmer and cook for 1 hour. Add the oregano, then keep cooking it until the meat wants to fall off the bone, about 2 1/2 hours. You will want to pull the head before it collapses, however, or things will get messy when you pick off all the meat.
2. If you are using nixtamal but not a pig's head, cover the corn with about 1 1/2 gallons of water and cook for 1 hour. Then add all the pork bits you have decided to put in your pozole. Simmer until tender as above. Once tender, break up the meat into bits you'd like to eat in a soup.
3. While this is happening, marinate the red onion in the 1/4 cup of lime juice. This removes any sulfur sting from the onion.
4. Once the corn is tender, add salt, but not before. Adding salt too early makes the kernels tough. After the meat and corn is all ready, or close to it, make it a green pozole by doing the following:

Making it Green

1. If you are using canned hominy, now is the time to stir it into the pot.
2. Cover the tomatillos with just enough water to cover and boil. Drop the heat to a bare simmer and let this cook for 15 minutes. Move the tomatillos to a blender and add to the blender the ground pumpkin seeds, epazote, hoja santa and sorrel (or any of these you happen to be using) and the chopped chiles. Buzz into a smooth puree; you might need to add some of the broth from the pozole.
3. Heat the lard in a Dutch oven or other large, heavy pot and add the blender mixture. Stirring constantly, cook this on medium-high for about 5 minutes, then scrape it all into the soup pot. Stir well, bring to a simmer and cook at least 10 more minutes, and up to 1 hour, but no more.
4. To serve, ladle out some pozole and let everyone top it with the marinated onion, avocado, cilantro and lime.