In a microwave-safe bowl add the onions, flour, basil, garlic, tomato paste. Drizzle with olive oil. Microwave for 4 minutes, stopping to stir every 90 seconds or so (it is expected that the mixture will be thick and pasty).
Add the mixture to the slow cooker, followed by the broth, tomatoes, sausage, and salt and pepper. Stir.
Slow cook on LOW for 4-6 hours.
When the soup is done slow cooking, warm the cream by placing in a sauce pan on low heat, slowly stirring, for about 3 minutes (you just want the cream warm enough so that it doesn’t start curding when added to the hot soup)
Add the cream, along with the tortellini, shaved parmesan and spinach. Slow cook on HIGH for about 10 minuetes.