In a large skillet, brown the Italian sausage with the chopped onion over medium heat for 7-8 minutes until fully cooked and the onions are translucent. Drain excess fat, then add minced garlic and sauté for another 30 seconds.

Transfer the sausage and onion mixture into your slow cooker, scraping in all the bits. Add chopped carrots, chopped celery, crushed tomatoes, diced tomatoes, and chicken broth. Stir to combine.

Cover the Crockpot and set it to cook on low for 7-8 hours or high for 3-4 hours.

About 30 minutes before the soup is done, stir in the cheese tortellini and heavy cream. Switch to high to warm it quickly.

In the last 10 minutes, fold in fresh baby spinach until just wilted.

Taste the soup and adjust the seasoning with salt and pepper. Serve in bowls with crusty bread.