Melt 2 tablespoons of butter in a large saucepan. Add chicken and sauté until meat is no longer pink. Transfer chicken to a plate and set aside (refrigerate.)
Melt an additional 2 tablespoons of butter in the saucepan and add onion, cumin, coriander and garlic; cook until onions are soft but not browned. Add corn, potatoes, chiles and broth; bring just to a boil. Lower heat, cover and simmer 20 minutes or until potatoes are tender.
Add milk. Puree half of the soup in a food processor or blender then return to the pan. Stir in the chicken. Heat until warmed through. Do not boil. Season with salt and black pepper. Yields 10 cups
