Create the Cookie Dough: Mix softened butter, eggs, vanilla extract, and cake mix until a soft dough forms. Add green food coloring to achieve the perfect festive shade.
Bake to Perfection: Scoop the dough onto a parchment-lined baking sheet and bake at 350°F for 8-10 minutes. Allow cookies to cool before assembling.
Whip Up the Mint Filling: Beat butter and marshmallow cream together, then add vanilla and mint extracts. Slowly mix in powdered sugar and milk until smooth.
Assemble the Whoopie Pies: Pipe the mint filling onto the bottom of one cookie, then sandwich it with another. Repeat with remaining cookies.