In a sauce pan over low heat combine flour and butter whisking for two minutes. Then slowing add in milk whisking unit well combined. Add in half of the cheese a small amount at a time until melted. Remove from heat.
Drain pasta pasta and pour into a casserole dish prepared with non-stick spray
Pour mixture evenly on top of pasta (you might have to stir the mixture around some)
Cover top with remaining cheese
Bake at 350 degrees for 30 minutes or until cheese is melted and bubbly