In a large frying pan over medium-high heat brown the Italian sausage with the onion for 4-5 minutes.
Add minced garlic and cook for 1 minute until fragrant.
In a 4-6 quart slow cooker add cooked sausage mixture, broth, potatoes, kale (or if you prefer more texture save to add with the cream at the end), salt and pepper.
Cook on low for 4-5 hours or high for 2 hours (cooking times vary by slow cooker).
Once potatoes are fork tender, stir in cream, Parmesan cheese and optional red pepper flakes. Add kale if not already in the soup.
Cook for another 30 minutes to heat through before serving.
Tips
When the soup is ready, use an immersion blender to blend the soup for a creamy soup.