Cheese Scalloped Carrots

Contributor:  Julie BeallCC Original 12 sliced and peeled carrots1/4 cup butter1 small onion1/4 tsp salt1/4 tsp dry mustard2 cups milk1/8 tsp pepper1/4 tsp celery salt1/2 lb sliced American or cheddar cheese Cook carrots, covered in boiling water, until barely tender.  Drain.  IN saucepan, cook onion