For an electric multi-cooker/pressure cooker: 

1. Wash hands with soap and water. Turn the sauté button on. Sauté oil and onions for 2-3 minutes. Add garlic and sauté for another 30 seconds. 
2. Turn sauté function off. Add chicken, stock, beans, chili powder, pepper, salt, and cumin. Secure the lid on the multicooker, ensure the pressure release valve is set on sealing. Use the manual or pressure cook button, set for 20 minutes. Allow for natural release for 10 minutes, then quick release.
3. Carefully remove lid, remove chicken. Using a food thermometer ensure the chicken is cooked to 165F. Shred chicken, and place back into cooker.
4. Combine cornstarch and water in a small bowl. Add sour cream, milk, and cornstarch and water mixture to multicooker. Turn multicooker back to sauté, and stir constantly to prevent burning and mix until soup starts boiling, turn off. Soup will thicken. Serve with cilantro if desired. 

Stovetop:

1. Wash hands with soap and water. Sauté oil and onions over high heat for 2-3 minutes.
2. Add garlic and sauté for 30 seconds, turn heat down to medium-high to medium, add chicken and ½ cup of stock or water or enough to cover chicken, and cook until chicken reaches 165F. Remove chicken and shred. 
3. Add stock, chilies, beans, and seasonings, bring to a boil. Once boiling, reduce heat to a simmer and cook uncovered for 30 minutes.

Combine cornstarch and water in a small bowl. Add sour cream, warmed milk, and cornstarch and water mixture to a pot of soup. While constantly stirring, return to a boil then reduce heat. Soup will thicken. Serve with cilantro if desired.

Store in airtight containers and refrigerate for up to four days. Freeze up to three months for best quality.