Prepare your cake batter as normal, and drop by tablespoonfuls onto a parchment-lined baking sheet (or bake in whoopie pie tins) for 11-13 mins, until done.
Cool fully on a wire rack, and beat together all filling ingredients.
Prepare sandwich-style, and serve!
Recipe by Happy Hour Projects at https://happyhourprojects.com/easy-whoopie-pies/