Reserve 1-1/4 cups broth. Bring remaining broth to a boil in a large pot, add tortellini and cook until tender, drain well.
In a small bowl, blend cornstarch into 1 1/4 cups of reserved broth.
In a large saucepan, saute garlic and basil in the butter or margarine for 2 minutes over a medium heat. Add the cornstarch-broth mixture to the saucepan. Cook and stir until the mixture thickens and comes to a boil.
Place tortellini in a serving dish, pour the broth-mixture, and Parmesan cheese into the serving dish and toss. Serve with toothpicks.
