2Cook the pork: Place the pork shoulder chunks in a large pot with 100 grams of white onion, 20 grams of garlic cloves, and 10 grams of salt. Cover with water and bring to a boil. Reduce heat and simmer for 60-90 minutes, or until the pork shoulder is tender. Remove the pork shoulder, shred it, and set aside. Strain and reserve 800 grams of the pork broth.
3Prepare the chiles: Lightly toast the ancho chiles and guajillo chiles in a dry pan over medium heat for 1-2 minutes until fragrant, being careful not to burn them. Place the toasted chiles in a bowl and cover with hot water. Let them rehydrate for 20-30 minutes until soft.