2Place 1000g pork shoulder in a large pot with 200g white onion, 30g garlic, 10g salt, and enough water to cover. Bring to a boil, then reduce heat and simmer until the pork shoulder is very tender, about 2-3 hours. Remove pork shoulder, reserving 200g of the cooking broth. Shred the pork shoulder once cool enough to handle.
3For the red chile sauce: Remove stems and seeds from 60g dried guajillo chiles and 40g dried ancho chiles. Toast the dried guajillo chiles and dried ancho chiles lightly in a dry pan for 30 seconds per side until fragrant, being careful not to burn them. Place toasted chiles in a bowl and cover with hot water. Let them rehydrate for 20-30 minutes until soft.