Place a large pot on medium-high heat. Add the sausage, onions, and garlic.
Cook, breaking up the sausage with a wooden spoon, until the meat is browned and the onions turn translucent, approximately 10 minutes. If needed, drain any excess fat.
Whisk in the chicken stock, crushed tomatoes, and tomato paste, ensuring everything is well combined. Bring the mixture to a boil, then add the salt. Lower the heat to a simmer and cook for about 15 minutes, allowing the sauce to thicken slightly.
Stir in the kale, spinach, tortellini, and cream. Continue cooking for 3-5 minutes, or until the kale has wilted and the tortellini is tender.
Spoon the soup into bowls. Add Parmesan cheese and red pepper flakes, if desired, before serving.