Spray the inside of a slow cooker with the nonstick cooking spray, add the sweet potatoes, onion, garlic, green chiles, rosemary, chipotle, salt, pepper and chicken broth and mix well. Cover and cook on low for 6-to-8 hours, or until the potatoes are very tender (so a fork can easily be pressed into them).

Remove about 1/4th the soup from the slow cooker and place it in a blender. Add 1/3 of the chopped tomatoes and blend until smooth. Pour the blended mixture into separate bowl, and repeat with the remaining soup. When finished blending, return all the blended soup back to the slow cooker, and cook for 15-30 minutes, or until it is warmed through.

To serve, spoon the soup into individual bowls, add a dollop os sour cream, and garnish with a few sprigs of cilantro. Serve hot.