Skillet Mac 'n Cheese

From the Kitchen of Cheryl Qualls

1/2 pound elbow macaroni (2 cups)
2 1/4 cups fat-free milk
2 Tablespoons cornstarch
1 cup shredded reduced-fat cheddar cheese (buy the sharp cheddar)
3 Tablespoons grated Parmesan cheese (Try the real stuff not the stuff in the shaker cans!)
2 teaspoons whole-grain Dijon mustard
1 teaspoon apple-cider vinegar
Pinch cayenne, or to taste
1/2 cup thinly sliced scallions (or not)

Cook the macaroni according to package directions, omitting the salt.
Meanwhile, to make the sauce, combine the milk and cornstarch in a large skillet, beating with a whisk until smooth. Bring to a boil over medium heat, about 3 minutes. Reduce the heat and simmer, stirring occasionally, until thickened, about 1 minute. Remove skillet from the heat; add the cheddar and Parmesan cheeses, mustard, vinegar, and cayenne, stirring until smooth.
Add the macaroni and scallions to the sauce; stir until combined and serve at once. Serving size is 1/2 cup. 3 points.