http://www.internationalrecipesonline.com/recipes/dictionary.pl?6485
1. A rich, velvety sauce made by combining BÉCHAMEL (white sauce) with
pureed cooked onions and sometimes a small amount of cream. 2. A meat
accompaniment of pureed cooked onions and rice. 3. A term applied to
dishes (such as eggs à la soubise) topped with or accompanied by a
creamy onion sauce.

A spelling bee word. More at Beheading Words