Though I tend not to use shortening, it does help create the nice dome of the whoopie pie. If you prefer, you could use all butter. Also, the cake layers tend to spread when baking. Don't worry, whoopie pies are meant to be a little irregularly shaped! Cake recipe adapted very slightly from Whoopie Pies : Dozens of Mix 'em, Match 'em, Eat 'em Up Recipes by Sarah Billingsley and Amy Treadwell. (A great book!) Filling from my elementary school PTA cookbook.
Recipe by MyUntangledLife.com at https://myuntangledlife.com/whoopie-pie-cake/