Preheat the oven to 375 and line two cookie sheets with parchment paper or silicone baking mat.
Using a standing mixer and whisk attachment, combine the cake mix, egg, and butter.
Beat until a soft dough forms.
Mix in 1 C of sprinkles.
Using a small cookie scoop, scoop out dough and roll it into a ball.
Pour the remaining sprinkles into a bowl and roll the dough ball in the sprinkles until completely coated.
Place the dough balls onto the cookie sheets and bake in the oven for 10-12 minutes. Remove from oven and allow to cool.
Using a standing mixer, beat the butter, powdered sugar, vanilla, heavy whipping cream, and a few drops of pink gel food coloring. Beat the butter until creamy and holds a peak.
Scoop the frosting into the piping bag.
Pair the whoopie pies up to make a sandwich and pipe frosting onto the bottom whoopie pie.
Place the top whoopie pie onto the frosting and gently press down. Enjoy.