Preheat oven to 350 degrees.
Melt butter in a large skillet over medium-high heat. Gradually whisk in flour until smooth. Cook, whisking constantly,for 2 minutes.
Stir in salt, both peppers, and granulated garlic. Gradually whisk in half-and-half and milk. Cook, whisking constantly, for 8 to 10 minutes or until thickened.
Stir in half of sharp Cheddar and all of extra-sharp Cheddar until smooth. Remove from heat.
Combine cheese mixture and pasta and pour into lightly greased 13-X-9-inch baking dish. Sprinkle remaining cheese on top.
Bake for 20 minutes. If you want a crusty top, bake for up to 15 more minutes.