Preheat the oven to 350 degrees. Prepare a 9 x 13 baking dish with nonstick cooking spray.

Cook noodles according to package directions until al dente.

In a large saucepan, melt the butter over medium-low heat. Add the flour and whisk until smooth. Slowly add milk, whisking continuously. Add the seasonings and bring to a boil, stirring constantly, until the mixture thickens enough that it coats the back of a spoon.

Add the cheeses and sour cream, stirring until melted. Immediately remove from heat.

Mix together the sauce and noodles. Transfer to the baking dish and top with additional white cheddar cheese if desired.

Bake for 15 minutes or until the cheese has melted and the edges bubble.