Preheat oven to 350°F. Add devil's food mix and water to a mixing bowl. With paddle attachment, mix on medium speed until combined. Do not over mix. Spray cookie sheet with cooking spray. Using a medium cookie scoop (1.25 oz), portion 1 scoop onto a sheet. Repeat until all the batter is portioned. Once portioned lightly lift, and drop sheet tray so batter spreads slighlty.Bake on 350 degrees for 15 minutes until cakes set. Allow to fully cool before handling.
Prepare Whoopie pie fillingUsing a mixer with whip attachment add the cream cheese to mixing bowl and whip until smooth. Add heavy cream, yogurt, vanilla and sugar and whip until smooth consistency. Whisk peppermint extract into the filling.
Fill a piping bag with a medium star tip and the peppermint cream cheese filling. Pipe 1 ounce of filling into the designated bottoms of the cakes. Top each cake lightly with the top.Heat the dark chocolate on the stove top over a double boiler or in the microwave. Place the formed cakes onto a sheet tray lined with a cookie rack or cooling rack. Drizzle 1 tbsp. of the melted chocolate over the top of the cakes. Allow to cool and rest for 15 minutes before serving.