Place a 5- to 8-pound pork shoulder, or similar cut, into a deep pot and cover with water. Bring the pot to a boil, then lower to a simmer and cook until very tender—at least 2 to 2½ hours.
For sabor (flavor), sauté together chiles guajillos (guajillo chilies), garlic, onion, clavos (cloves), comino (cumin), pepper, a little oregano and a tiny bit of cinnamon.
Once the mixture is cooked and cooled, blend and strain it to eliminate chunky pieces. Stir it into the cooked and shredded meat with chiles rojos (red chilies) as filling for tamales.