Combine all ingredients in a slow cooker. Cover and cook on low for 5-7 hours, until flavors are blended and vegetables are soft. Allow the soup to cool slightly. using an immersion blender, blend the soup until smooth. Or puree in batches in a blender. Serve immediately, or keep on low until ready to eat.
Combine all ingredients in a heavy lidded pot or dutch ovenover medium-high heat. Bring to a boil, then turn heat down to low, and simmer, covered, for about 2 hours, until flavors are blended and vegetables are soft. Allow the soup to cool slightly. Then puree as instructed above.Garnish with fresh basil and Parmesan cheese.
If you like a creamier version, omit about 1 cup of the chicken broth and add milk or half and half.