Preheat oven to 350°F
Combine chocolate cake mix, oil, and eggs until combined. Form into one-inch balls and place baking sheets lined with parchment paper. Bake for 6 minutes then remove from oven and place one-half of a marshmallow on top of each cookie (sticky side of marshmallow facing down). Bake for another two minutes and remove from oven. Gently smash the marshmallows down with a spatula and remove cookies to a cooling rack.
Meanwhile, combine sugar, milk and butter in a saucepan-melt and bring to a boil. Remove from heat and stir in chocolate chips and peppermint chips. Continue stirring until smooth. Frosting should thicken up.
Pour frosting over the top of each cookie, then sprinkle a few peppermint chips over the top.
Cookie adapted from Me Oh My