1Place pork shoulder in a large pot with enough water to cover. Add 5g salt and half of the 150g white onion. Bring to a boil, then reduce heat and simmer until the pork shoulder is very tender, about 1.5 to 2 hours.
2While the pork shoulder cooks, remove stems and seeds from dried ancho chiles and dried guajillo chiles. Place the chiles in a heatproof bowl and cover with hot water. Let them rehydrate for 20-30 minutes until softened.
3Drain the rehydrated chiles, reserving a small amount of the soaking liquid. In a blender, combine the rehydrated chiles, 30g garlic cloves, the remaining half of the 150g white onion, apple cider vinegar, ground cumin, dried Mexican oregano, black peppercorns, and whole cloves. Add about 100g of the pork cooking liquid or chile soaking liquid to help blend. Blend until a smooth paste is formed.
