Melt butter in a large skillet over medium-high heat. Gradually whisk in flour until smooth; cook, whisking constantly, 2 minutes. Stir in salt and next 3 ingredients. Gradually whisk in half-and-half and milk; cook, whisking constantly, 8 to 10 minutes or until thickened.
Stir in half of sharp Cheddar cheese. Stir in extra-sharp Cheddar cheese until smooth. Remove from heat.
Combine pasta and cheese mixture, and pour into a lightly greased 13- x 9-inch baking dish. Sprinkle with remaining sharp Cheddar cheese.
Bake at 350° for 20 minutes (bake 15 minutes longer for a crusty top). Prep: 35 min., Bake: 35 min.
NOTE: For testing purposes only, we used Kraft Cracker Barrel cheeses.