Melt the butter over low heat.
As soon as the butter melts, slowly add the flour and whisk until smooth and there are no longer any lumps.
Now add the milk very slowly and stir again very vigorously.
Continue to slowly add the milk as you whisk.
Let the sauce cook and simmer for 7-8 minutes or until it becomes thick. Don't forget to stir, and don't let it boil over.
Add a little salt, pepper, 1 cup cheddar cheese, and 1/2 tsp chili powder while it's cooking.
Turn off the heat and stir in the chicken mixture and cooked macaroni.
Pour pasta into a sprayed 9x13 baking dish .
Top with 1 cup of cheese and crushed crackers.
Bake at 400 degrees for about 20 minutes or until cheese is melted and crackers are browned.