1. Preheat oven to 400 degrees F.
2. In medium pan, saute onion with butter.
3. Add milk, salt and pepper into pan gradually while stirring.
4. In separate pan, cook noodles and drain.
5. In greased casserole pan, layer noodles, chicken, and broccoli.
6. Pour onion mix over top and sprinkle cheese over.
7. Bake 20 minutes