Heat the olive oil in a large stockpot or Dutch oven over medium heat until it shimmers. Add the Italian sausage and cook for 3-5 minutes, breaking it apart with a wooden spoon until browned and crumbled. If there's more than 1-2 tablespoons of fat, drain the excess, keeping about 1 tablespoon in the pot for flavor.

Stir in the minced garlic, diced onion, and Italian seasoning. Cook for 2-3 minutes, stirring frequently, until the onions turn translucent and the garlic becomes fragrant. Season with salt and pepper at this stage.

Sprinkle the flour over the sausage mixture and whisk continuously for about 1 minute until it turns lightly golden to create a roux.

Pour in the chicken stock and tomato sauce, stirring well to incorporate. Add the Parmesan rind if using. Bring the mixture to a boil, then reduce the heat and simmer for about 10 minutes, stirring occasionally, until the soup thickens slightly and coats the back of a spoon.

Add the tortellini to the pot, cover with a lid, and cook for 5-7 minutes until tender, following package instructions for timing.

Stir in the chopped kale and cook for 1-2 minutes until it wilts and turns bright green.

Remove and discard the Parmesan rind. Stir in the heavy cream and chopped basil, cooking for just 1 more minute until everything is heated through. Taste and adjust seasoning with additional salt and pepper if needed.

Ladle into bowls and garnish with fresh parsley. Serve immediately while hot.