Add all ingredients EXCEPT the cornstarch and cheddar to the slow cooker. Stir to combine and secure lid. Cook on HIgh for 4-6 hours (or Low 6-8 hours)
Remove chicken and shred or chop.
Stir soup to incorporate the cream cheese fully. Then remove about 2 cups of soup to a bowl. Blitz with an immersion blender until smooth. Add cornstarch and blitz again to combine. Return to slow cooker, along with shredded chicken.
Add three cups of cheese (one cup at a time) and stir until melted.