Preheat oven to 350 degrees.
Mix the cake mix, pumpkin, egg, and pumpkin pie spice until it is all well combined.
Spoon generous spoonfuls of batter onto a cookie sheet covered in wax paper. Make sure they are at least 2 inches apart. Swirl the batter with your spoon to make them more round.
Tap the cookie sheet a few times to smooth out your cookie batter.
Bake at 350 degrees for 10 minutes. Move the cookies to a wire rack to cool.
In mixing bowl, whip the butter for a few minutes.
Add in the powdered sugar, vanilla and 1 tablespoon of milk. Beat for 3-5 minutes, adding in another tablespoon of milk if the frosting needs to be thinner.
Cut chocolate bar into pieces.
Place frosting in a piping bag and pipe onto the cookies.
Sprinkle the top with dark chocolate pieces. Store in refrigerator or air tight container.