3. Place potato slices and onion in a 5-quart electric slow cooker coated with cooking spray.
4. Combine 1/2 cup water and next 3 ingredients (through pepper); stir into mixture in slow cooker. Cover and cook on LOW for 8 hours or until potatoes are tender.
5. Mash mixture with a potato masher; stir in milk and 3/4 cup cheese.
6. Increase heat to HIGH. Cover and cook on HIGH for 20 minutes or until mixture is thoroughly heated.
7. Ladle soup into bowls. Top with sour cream and remaining 1/4 cup cheese. Sprinkle with bacon and chives.