The copper pots they are cooked in often come from Santa Clara del Cobre, a Michoacán town whose copperwork goes back to the Purépecha.
Pork is slowly simmered in its own lard in big copper cazos until tender with crisp edges, then chopped to order at stalls and sold by weight or in tacos with salsa and onion.
Why it's made this way: Michoacán is widely credited as the home of carnitas, and the town of Quiroga, lined with carnitas vendors, calls itself the carnitas capital of the world.