Preheat oven to 375°F.
Spray a 9x13-inch pan with cooking spray and set aside.
Cream the shortening and sugar. Add egg and beat thoroughly. Add molasses, sweet potato, and orange zest.
Sift together the all-purpose flour, salt, baking soda, baking powder, and ginger. Stir in whole wheat flour. Add dry ingredients alternately with buttermilk to the sweet potato mixture, starting and ending with flour mixture.
Spread in prepared pan and bake for 45 to 50 minutes, or until cake tester comes out clean.
While warm, cut into 54 bars (9 by 6 rows)
Recipe submitted by Mark on 5/26/00