Heat olive oil in a large stockpot or Dutch oven over medium heat. Add Italian sausage and cook until browned, about 3-5 minutes, making sure to crumble the sausage as it cooks; drain excess fat.
Stir in garlic, onion and Italian seasoning. Cook, stirring frequently, until onions have become translucent, about 2-3 minutes; season with salt and pepper, to taste.
Whisk in flour until lightly browned, about 1 minute.
Stir in chicken stock, tomato sauce and Parmesan rind, if using. Bring to a boil; reduce heat and simmer, stirring occasionally, until reduced and slightly thickened, about 10 minutes.
Stir in tortellini; cover and cook until tender, about 5-7 minutes.
Stir in kale until wilted, about 1-2 minutes. Stir in heavy cream and basil until heated through, about 1 minute; season with salt and pepper, to taste.
Serve immediately.
Notes
Use refrigerated tortellini. Fresh refrigerated tortellini tastes much better than dry tortellini and cooks up so much faster.
Save leftover Parmesan rinds. Get more out of those expensive Parmesan cheeses by using up the leftover rinds! Adding a Parmesan rind slightly thickens the broth and adds a level of nutty richness to the soup.
Add in leafy greens. This is a great recipe to sneak in leafy greens for those picky eaters. Spinach, kale, collard greens, swiss chard, or arugula are all great options.
Add the cream slowly. Always add the heavy cream at the very end, pouring very slowly to prevent curdling.
Store tortellini separately for leftovers. When planning for leftovers, store the cooked tortellini separately from the soup to prevent it from soaking up all the broth.
Serve with crusty bread. Serve with homemade crusty bread or garlic knots for dipping—classic sides for creamy tortellini soup.