1Place the Beef shank in a large pot with 3000g of Water, half of the White onion, 10g of Garlic cloves, and the Bay leaf. Add 10g of Salt. Bring to a boil, then reduce heat, skim any foam, and simmer for 2 to 2.5 hours, or until the Beef shank is very tender. Remove the Beef shank, shred the meat from the bone, and set aside. Strain the beef broth and reserve.
2While the beef cooks, prepare the chiles. Remove stems and seeds from the Ancho chiles, Guajillo chiles, and Pasilla chiles. Lightly toast the chiles in a dry pan over medium heat for 30 seconds per side until fragrant. Be careful not to burn them. Transfer the toasted chiles to a bowl and cover with hot water. Let them rehydrate for 20 minutes.
3In a separate pot, boil the Roma tomatoes with the remaining White onion and Garlic cloves until softened, about 10 minutes. Drain and set aside.
