Step 1: Heat 1 tablespoon of olive oil in a large Dutch oven or heavy-bottomed pot over medium heat. Add the Italian sausage, breaking it up with a spoon, and cook until browned and crumbled, about 5-7 minutes. Drain any excess grease and set the cooked sausage aside.
Step 2: Add the remaining 1 tablespoon of olive oil to the pot. Add the chopped onion and cook until softened and translucent, about 5 minutes. Add the minced garlic and cook for another minute until fragrant, being careful not to burn it.
Step 3: Stir in the dried oregano and red pepper flakes (if using) and cook for 30 seconds until fragrant.
Step 4: Pour in the crushed tomatoes, chicken broth, and reserved cooked sausage. Bring the mixture to a gentle simmer, then reduce the heat to low, cover, and let it simmer for at least 15-20 minutes. This allows the flavors to meld beautifully. For an even richer flavor, you can let it simmer longer.
Step 5: Increase the heat to medium-low and add the fresh spinach, stirring until it wilts, which should only take 2-3 minutes.
Step 6: Stir in the heavy cream and fresh basil. Bring the soup back to a gentle simmer. Do not boil once cream is added, as it can curdle.
Step 7: Add the fresh tortellini to the simmering soup. Cook according to package directions, typically 3-5 minutes, until the tortellini is al dente and floats to the top. Overcooking will make the tortellini mushy, so keep a close eye on it.
Step 8: Season the soup with salt and freshly ground black pepper to taste. Taste and adjust seasonings as needed.
Step 9: Ladle the creamy tomato basil tortellini soup into bowls. Garnish with freshly grated Parmesan cheese and extra fresh basil leaves, if desired. Serve immediately and enjoy.