In a large pot, bring 2 ½ cups broth to a boil. Add cheese tortellini. Return to a boil and cook until the tortellini float to the top of the water, about 3 minutes. The internal temperature of a tortellini should be 165 degrees. Drain completely.
Meanwhile, whisk together remaining 1 ½ cups broth with corn starch. In a large non-stick skillet, melt butter over medium-high heat until foaming. Stir in garlic and basil and cook 2 minutes.
Add broth-cornstarch mixture and bring to a boil; simmer until the mixture thickens, about 2 minutes longer. Add the cooked tortellini to the skillet and toss to coat.
Pour into a serving dish and garnish with Parmesan cheese and fresh basil, if desired.
