Preheat oven to 375°.
Whisk together 1 cup milk and flour in a saucepan; add remaining 1 1/2 cups milk, stirring well. Cook, stirring constantly, over medium heat 8 minutes or until bubbly. Reduce heat to low; add butter and next 4 ingredients. Cook, stirring constantly, 2 minutes. Stir in pasta; spoon into a 2-quart casserole coated with cooking spray. Sprinkle with breadcrumbs.
Bake at 375° for 30 minutes or until bubbly.