• Cut pork shoulder into 1 1/2 to 2-inch cubes. Season generously with kosher salt. Warm oil in a large cast-iron pot over medium-high heat. I've actually got an All-Clad Delux Slow Cooker with removable cast-iron insert, so I just use that. Brown pork in batches, making sure you don't crowd the pan. Browning just 2 sides is sufficient, and transfer to a plate when finished. This should take 8 to 10 minutes per batch.
• Add onion and garlic to the hot oil with a pinch of salt, and cook, stirring occasionally, until tender and fragrant (4 to 5 minutes). Stir in the dried black beans, bay leaves (or epazote), water and browned pork. Bring the mixture to a boil, then take off the heat. If you're using a slow cooker insert, simply transfer the insert to the slow cooker. If you're using a cast-iron pot, transfer the contents to a slow cooker. Cook on low until the beans and pork are tender (6 to 8 hours). During the last hour of cooking, season to taste with kosher salt (I added about 2 1/2 teaspoons).

To serve, ladle soup into a bowl, then top with chopped onion, radish and cilantro. Serve with lime wedges and warm corn tortillas.