Add tomatoes, chicken broth, onions, garlic, salt, pepper, and sugar to the slow cooker and cook on high for 4 hours.
After the 4 hours, add in the chopped basil leaves.
Using either an immersion blender or a stand blender, blend soup until smooth.
(If you used a regular stand blender return the soup to the slow cooker)
After blended, add in the cream.
Stir to combine.
Cook for 30 more minutes.
Top with the parmesan cheese and enjoy!! (I like to serve mine with croutons and a little extra basil on top)