Cook the first four ingredients in your slow cooker on low for 4 hours.
When the pumpkin is soft and cooked through, use a hand blender, immersion blender, or food processor to blend in the remaining ingredients.
Sprinkle a little cayenne pepper on top when serving, if desired.
If canned pumpkin is used, use 2 (15-ounce) cans.Skim milk is NOT recommended (use more or less milk depending on thickness preferred), the amount of milk will depend on desired consistency of soup. If you like soup a little on the thinner side, add 3 cups of milk.