Preheat oven to 350°. In a medium sauce pan over medium heat, melt butter. Add flour 1 tablespoon at a time; whisk between each addition. Cook while whisking constantly to prevent mixture from burning. Add milk a half cup at a time, whisking slowly to thicken. Add fresh cracked pepper.
Reserve 1⁄2 cup of cheese for topping. Add cheese to roux and stir until incorporated. In a bowl, add cheese mixture, chicken, cauliflower and macaroni and mix until incorporated. Put into buttered baking dish and top with reserved cheese and crushed croutons. Bake for 25 minutes until bubbly and light brown on top.