In a large pot or Dutch oven, heat olive oil over medium-high heat. Add Italian sausage and cook, breaking it up with a spoon, until browned.
Add onion and garlic to the pot and cook until softened, about 5 minutes.
Pour in chicken broth and bring to a simmer. Add thyme, red pepper flakes (if using), salt, and pepper.
Reduce heat to low and simmer for 15 minutes to allow flavors to meld.
Stir in heavy cream and Parmesan cheese. Cook until heated through, about 5 minutes.
Serve hot and enjoy!
Notes
For a thicker soup, you can add a slurry of cornstarch and water (1 tablespoon cornstarch mixed with 2 tablespoons cold water) during the last few minutes of cooking. Garnish with fresh parsley or additional Parmesan cheese, if desired.