Preheat oven to 350 degrees – start the elbow macaroni boiling.
melt butter in a saucepan over med heat. Add flour and wisk until combined
Add milk a little at a time, wisking each time until smooth until all the milk is added
Heat to boiling, adding a shake or two of salt and pepper, then turn down the heat and let cool slightly.
By now your macaroni should be cooked. Drain and return to pot over low heat and add the white sauce. Add your pieces of cheese and stir until mostly melted. then add chicken and broccoli and stir well.
Transfer cheesy macaroni to a 9×13 pan. Put slices of butter anywhere (to help the crust cook evenly)
Sprinkle lightly (or heavily if your like my family and love a serious crust on your macaroni!) with Italian Seasoned Breadcrumbs.
Place in preheated oven for about 30 minutes, or until the crust is lightly browned.