Heat a large heavy bottom Dutch Oven over medium high heat. Add Italian sausage and cook until browned, about 5-6 minutes, making sure to break up the sausage as it cooks.
Stir in the onion and Italian seasoning once the sausage has cooked and season with salt and pepper, to taste. Cook until onions are translucent. Add the garlic and sauté for about 30 seconds more.
Whisk in flour and cook for about 1 minute. Pour in the chicken stock and tomato sauce and bring the mixture to a boil. Reduce heat and simmer, stirring occasionally, until reduced and slightly thickened, about 10 minutes.
Stir in tortellini and kale cook until the pasta is tender and the kale is wilted, about 5-7 minutes. Stir in heavy cream, cheese until heated through, about 1 minute and season with salt and pepper to taste. Stir in basil right before serving and add extra cheese on top if desired.