Preheat oven to 375 degrees 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 rind.
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 toothpick inserted in center comes out clean. While warm, cut into 54 bars (9 by 6).