Brown the Sausage
In a large soup pot or Dutch oven, heat olive oil over medium heat. Add Italian sausage and cook, breaking it into crumbles, until browned and fully cooked. Drain excess fat if needed.
Sauté the Vegetables
Add the diced onion, garlic, carrots, and celery to the pot. Cook for 5–6 minutes until softened and fragrant.
Add Seasonings and Tomatoes
Stir in Italian seasoning, red pepper flakes, and crushed tomatoes. Cook for 2 minutes to allow flavors to develop.
Pour in Broth and Simmer
Add chicken broth, season with salt and pepper, and bring the soup to a boil. Reduce heat and simmer for 10–15 minutes until vegetables are tender.
Cook the Tortellini
Add tortellini to the soup and cook according to package instructions, typically 4–7 minutes, until tender.
Add Greens and Cream
Stir in spinach (or kale) and let it wilt. For a creamy soup, stir in heavy cream and let it heat through for 1–2 minutes.
Serve
Ladle into bowls and top with grated Parmesan and fresh herbs. Serve with crusty bread if desired.