Add chicken broth, tomatoes, butter, onions and garlic to slow cooker.
Cook on high for about 5 hours, or on low 7-8 hours.
Onions will be soft and translucent when ready.
Use an immersion blender to blend until smooth.
Add cream and stir to combine.
Season with salt and freshly ground pepper to taste.
Recipe Notes
You can also use a regular blender. Just blend hot soup in small batches. Vent blender so steam can escape and keep dish towel over vent to stop splatters.