Cover and cook on Low for 4 to 6 hours or High for 2 to 3 hours, until chicken is cooked through and shreds easily.
Remove chicken, shred with two forks, and return it to the soup.
Let soup simmer another 10 to 15 minutes on Low or Warm.
Serve hot with sour cream, cheese, cilantro, and tortilla chips.
Notes
Add a splash of chicken broth when reheating if the soup thickens in the refrigerator. Do not add tortilla chips or sour cream before freezing. The soup keeps refrigerated for up to 5 days and freezes well for up to 3 months. Day two tastes even better as the flavors settle.