Preheat oven to 350 degrees. Spray 9 x 13 inch baking pan with cooking spray.
Cook shells according to package directions for al dente. Drain. Set aside.
Melt butter in a medium saucepan over medium-low heat. Stir in flour. Gradually stir in milk and half and half. Stir continuously over medium heat until mixture thickens. Lower heat. Stir in cheeses and seasoings. Mix until completely melted. Remove from heat. Stir in shells. Pour into prepared pan. Bake for 30-40 minutes or until hot and bubbly.