In a large pot or Dutch oven, heat the olive oil over medium-high heat. Add the sausage and cook until the meat starts to brown, breaking it up with a wooden spoon, about 2 minutes. Add the onion and garlic; cook, stirring, until the sausage is no longer pink and the onion softens, about 3-5 more minutes. Drain off the excess grease.
Stir in the broth, diced tomatoes with their juices, tomato sauce, Italian seasoning, and sugar. Bring the mixture to a boil; cover, reduce the heat to low, and simmer covered for 15 minutes.
Remove the lid, add the tortellini, and cook according to the package directions for al dente, about 3-5 minutes. Reduce the heat to the lowest setting. Stir in the cream and cook just until warmed through, about 1-2 more minutes. Add the spinach (if using) and let it wilt in the hot broth for about 30-60 seconds. Taste and season with salt and pepper, if desired.
Ladle into bowls and garnish with Parmesan cheese and fresh herbs.