Add all ingredients EXCEPT the heavy cream to the slow cooker. Stir to combine and secure lid. Cook on low for 5½ hours.
Remove chicken from slow cooker and chop into bite-sized pieces. Remove half of soup to a separate bowl. Return chicken to slow cooker.
Add heavy cream to soup transfered to separate bowl. Use an immersion blender to blitz until smooth. return to slow cooker and stir to combine. Secure lid and let cook for remaining 30 minutes.