Slow-Cooker Creamy Cauliflower Soup

Place first 10 ingredients in a 6-qt. slow cooker. Add water; sprinkle milk powder over top., Cook, covered, on low until cauliflower is very tender, 6-8 hours. Remove bay leaf. Puree soup using an immersion blender. Or cool slightly and puree soup in batches in a blender; return to slow cooker and heat through. If desired, serve with toppings.