Heat olive oil in a large cast iron skillet over medium high heat. Add Italian sausage and cook until browned, about 3-5 minutes, making sure to crumble the sausage as it cooks; drain excess fat.
Place Italian sausage into a 6-qt slow cooker. Stir in chicken stock, diced tomatoes, tomato sauce, onion, garlic, Italian seasoning and Parmesan rind, if using; season with salt and pepper, to taste.
Cover and cook on low heat for 7-8 hours or high heat for 3-4 hours.
Uncover and stir in tortellini, kale and heavy cream; cover and cook on high heat for an additional 20-30 minutes, or until tortellini is tender. Stir in basil; season with salt and pepper, to taste.