Add first 9 ingredients (through broth) to a slow cooker/crockpot. Cover and cook for 2 hours on high or 4-8 hours on low.
Step 2
About 30-40 minutes before serving transfer soup to a blender or food processor and puree until smooth, then return to crock pot.
Step 3
Prepare the roux. Melt butter in a medium sauce pan over medium heat. Add flour to melted butter and stir until flour clumps up. Slowly whisk in the heavy cream (or half & half) until mixture is thickened and smooth.
Step 4
Add roux and parmesan cheese to crockpot and stir to combine.
Step 5
Top with additional basil and parmesan cheese if desired.
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