Set a large 6-8 quart soup pot over medium heat. Melt the butter in the pot. Then add the ground Italian sausage, onions, and garlic. Use a wooden spoon to break the ground sausage into small pieces. Cook for 5 to 10 minutes until the onions are soft and the sausage is fully browned.
Add the dried thyme, chicken broth, diced tomatoes, and tomato paste. Cover the pot and bring to a boil. Then lower the heat, if needed, and simmer for 10 minutes.
Stir in the tortellini and Parmesan cheese. Simmer for about 5 minutes, until the tortellini rises to the top of the pot.
Then turn off the heat and stir and heavy cream and basil leaves. Taste, then salt and pepper if needed.
