Preheat oven to 350 degrees.
In a bowl or stand mixer, cream together butter and cream cheese until smooth.
Add egg and beat until smooth. Add cake mix and mix until combined.
Scoop approx 1.5 tablespoons of dough (medium cookie scoop) and round into ball.
Roll in powdered sugar to coat. Place on lightly greased cookie sheet.
Bake for 10 minutes until puffed and cracked but still quite soft.
Leaving cookies on cookie sheet, place a Mint Truffle Candy Kiss on each cookie, pressing down slightly, and allow to melt (return to oven for 60 seconds if needed).
Remove cookies to cooling rack.
Melt green mint chips or candy melts and drizzle over cookies.