Spray 4- to 5-quart slow cooker with cooking spray. In cooker, mix all ingredients except whipping cream and parsley.
Cover; cook on Low heat setting 8 to 10 hours.
Blend soup in cooker with immersion blender, or blend soup in batches in blender container on low speed and return to cooker. Stir in whipping cream. Sprinkle each serving with parsley.