Melt butter in a Dutch oven over medium heat; whisk in flour until smooth. Gradually whisk in milk, and cook, whisking constantly, 3 minutes or until thickened. Add Cheddar cheese, 1/4 cup Parmesan cheese, salt, black pepper, and red pepper, whisking until cheese melts. Add pasta, tossing to coat. Pour mixture into a lightly greased 13- x 9-inch baking dish. Sprinkle with remaining 1/2 cup Parmesan cheese.
Bake at 350° for 5 minutes or until cheese melts.