I typically use shoulder meat from a wild hog for this recipe, but regular pork shoulder or ribs are all common in Mexico. Most of the ingredients here are easy to find, but I'll offer some substitutions below.
2 to 5guajillo chiles, seeded, stemmed and rehydrated
2 to 5ancho chilesseeded, stemmed and rehydrated
2 to 5chiles morita, or chipotles in adobo
3tablespoonslard or vegetable oil
Crema or sour cream to taste
Cover the pork shoulder with water in a large, lidded pot like a Dutch oven. Bring to a boil, then drop to a simmer. Skim off any scum or froth that develops. Add the remaining braise ingredients, cover the pot, turn the heat to low and simmer gently until the pork is tender -- anywhere from 90 minutes for some store bought pork to 3 hours for an old wild hog.
Meanwhile, get a comal, griddle or cast iron pan hot and sear the onion, cut side of the tomatoes and garlic until well blackened. While this is happening, rehydrate the chiles with hot water after you have seeded and stemmed them.
When the vegetables are well charred, discard the garlic peels and put everything in the blender, along with the chiles -- discard the chile water. Add the tomatillos and a pinch of salt and puree. If you want to, push the salsa through a fine mesh sieve into a bowl to remove any bits of skin and seed, which are undigestible.
Heat the lard in a sauté pan and pour the salsa in. It will spit and sputter. Stir this constantly until the lard is incorporated, then turn the heat to low and cover the pot.
When the pork is tender, strain the broth and reserve. Slice the pork across the grain here and there so you don't have long, stringy pieces. Wipe out the pot, then return the pork, strained broth to it, adding the salsa and the purslane. Simmer this for about 10 to 20 minutes, adding salt to taste.
Serve with the crema alongside, with some hot sauce, and tortillas.
If you can't find the exact chiles, any combination will do. Other good ones are pasillas, chiles negro, chiles California, and dried red Hatch chiles. For the spicier moritas, you can usually find the chipotles in adobo. If not, any hot chile will do.
If you want to make this and can't find purslane, use any quelite, or wild edible green. Lambsquartersis a great option.
While this is mostly done with pork, venison or any other red meat will work well, and there is a version done with jackrabbit in Sonora. Wild turkey legs would be good, too.
If you cook this down so it's not quite as stewy, you can use this as a taco filling.