Coat 9”x13” baking dish with cooking spray. Line dish with 6 slices of bread. Layer half the ham over the bread and sprinkle with 1 cup cheese; repeat layers once more. In a large bowl, combine eggs, milk, dry mustard, onion powder, salt and pepper; mix well. Slowly pour over entire casserole. Mix butter with cornflakes and sprinkle on top. Bake at 350 degrees for 45-50 minutes or until golden and set.