This recipe is from Shirley McNevich's Mom's Best Recipes Vol 5. Published here with her permission.
Don't forget to check Shirley's blog.
(by Aunt Isabelle "Snooky" [McNevich] Worhach)
2 cups white sugar
1 cup mayo
1/2 cup Hershey's cocoa
1 cup leftover mashed potatoes
1 2/3 cup flour (sifted--measure before sifting)
1 tsp. baking soda
2 tsp. vanilla
1/2 cup buttermilk
In a mixer add white sugar, mayo, and eggs--beat. Add mashed potatoes--
beat. Add cocoa, baking soda and vanilla--beat. Add buttermilk and flour--
beat. Pour batter into a greased 9 x 13 cake pan. Bake at 350 degrees for
30-40 minutes--test with a toothpick for doneness. Frost as desired.