Thought to be of Pennsylvania Dutch origin, the extremely sweet filling of a shoofly pie is a mixture of molasses, brown sugar, water and butter. There are several different stories concerning the origin of the pie's name. One is that it's so sweet that one must shoo away the flies; another declares that the pie was originally made to attract flies away from other foods.
From The Food Lover's Companion, Fourth edition by Sharon Tyler Herbst and Ron Herbst. Copyright © 2007, 2001, 1995, 1990 by Barron's Educational Series, Inc.