Grease crockpot with cooking spray.
Place sweet potatoes, carrots, broth, apple, onion, garlic, salt, cayenne, and pepper into crockpot.
Stir to combine.
Place on lid and cook on HIGH for 3-4 hours or LOW 6-8 hours.
Stir in milk.
Working in batches, blend soup into a high-powered blender until smooth.
Serve and enjoy!